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C# Win8: copy .PNG to the Windows clipboard; paste with transparency preserved

I have been tasked with capturing an image, copy it to the clipboard, and paste it to the application below. I must be able to support pretty much any rich text field, and it must preserve transparency. My current solution first renders a white background. Here is my code:
The RenderTargetBitmap contains the image that I wish to copy as a .PNG
public static void CopyImageToClipboard(RenderTargetBitmap b)
{
MemoryStream stream = new MemoryStream();
PngBitmapEncoder encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(b));
encoder.Save(stream);
Bitmap bmp = new Bitmap(stream);
Bitmap blank = new Bitmap(Convert.ToInt32(b.Width), Convert.ToInt32(b.Height));
Graphics g = Graphics.FromImage(blank);
g.Clear(System.Drawing.Color.White);
System.Drawing.Image img = System.Drawing.Image.FromStream(stream);
g.DrawImage(img, 0, 0, Convert.ToInt32(b.Width), Convert.ToInt32(b.Height));
Bitmap tempImage = new Bitmap(blank);
blank.Dispose();
img.Dispose();
bmp = new Bitmap(tempImage);
tempImage.Dispose();
System.Windows.Forms.Clipboard.SetImage(bmp);
stream.Dispose();
}

Just pick a random color to use it as background, let's say
var background = Color.FromArgb(1, 255, 1, 255);
Erase background to it:
g.Clear(background); // instead of System.Drawing.Color.White
Then make that color transparent:
Bitmap tempImage = new Bitmap(blank);
tempImage.MakeTransparent(background);
Note that also default transparent color works pretty well, no need to pick a magic color (check if you need to Clear() background, it may be - I didn't check - default bitmap background):
g.Clear(Color.Transparent);
// ...
tempImage.MakeTransparent();
EDIT Some older RTF control versions won't handle transparency and there is nothing (AFAIK) you can do for it. A half decent workaround (if you can't detect control class of paste target and read its background color) is to use Color.FromArgb(254, 255, 255, 255). White where transparency isn't supported and...completely transparent (because of MakeTransparent()) where it is.

The Windows clipboard, by default, does not support transparency, but you can put content on the clipboard in many types together to make sure most applications find some type in it that they can use. Generally, if, in addition to the normal nontransparent clipboard Bitmap format, you put the image on the clipboard in both PNG and DIB formats, most applications will be able to use at least one of them to get the image in a format they support as being transparent.
These formats are put on the clipboard in a specific way, though. They need to have their data (for png, that's not the loaded image object but the actual png file's bytes) put in a MemoryStream that is then put on the clipboard.
PNG put on the clipboard like that will be accepted by a multitude of applications, including Gimp and the newer MS Office. And of course, if you implement reading for it too, you can use it in your own application. The (rather dirty) DIB format should take care of most other applications, if they indeed support transparent image pasting at all.
I detailed how to do both the copying and the retrieving in this answer:
https://stackoverflow.com/a/46424800/395685

Put .Gif Image from Clipboard to PictureBox

I want to copy gif image from Browser and paste to PictureBox
Image cImage = Clipboard.GetImage();
pictureBox1.Image = (Image)cImage;
This put image, but its not animated.

The image on the clipboard isn't a GIF, it's a Bitmap or DIB (or both). Those are the formats that you would see, if you used the old XP Clipboard Viewer (clipbrd.exe), or if you enumerated the available clipboard formats within your program.
See the list of standard clipboard formats: http://msdn.microsoft.com/en-us/library/windows/desktop/ff729168(v=vs.85).aspx
GIF is not one of them.
Also, there is no JPG or PNG. When you copy those images, they're placed onto the clipboard as CF_BITMAP and/or CF_DIB. Basically, Bitmap is the universal image format that everything converts to/from.
As an alternative, you MAY be able to get CF_HTML from the clipboard, figure out where the image is, and then fetch it from the server (or maybe the browser cache), preserving the original GIF information.

Windows API Code Pack - ShellFile not generating PDF bitmap

Using the code from previous stack overflow questions:
System.Drawing.Bitmap image;
ShellFile f = ShellFile.FromFilePath(fileLocation);
image = f.Thumbnail.ExtraLargeBitmap;
image.Save(tempfile, ImageFormat.Png);
I am trying to use window API to get the thumbnail of a PDF
I am led to believe that this generates an image file that resembles the first page of the PDF document.
The reality however is that it does NOT look like that, and merely looks like the PDF icon.
Is there anything that I'm missing that is required before this actually works as intended?
PDF files are correctly associated with adobe reader.
When browsing directories in windows explorer I DO see thumbnails associated with the documents.
I should note that the code DOES in fact correctly extract thumbnails when dealing with Excel and Word documents.
EDIT (references):
C# get thumbnail from file via windows api
Get thumbnail of any file, not only image files on Windows XP/Vista
Windows API Code Pack Thumbnail gives preview thumb of pdf but not Word or Excel

You need to specify that you want the thumbnail, not the icon (the default).
Change your code into this:
System.Drawing.Bitmap image;
ShellFile f = ShellFile.FromFilePath(fileLocation);
//force the actual thumbnail, not the icon
f.Thumbnail.FormatOption = ShellThumbnailFormatOption.ThumbnailOnly;
image = f.Thumbnail.ExtraLargeBitmap;
image.Save(tempfile, ImageFormat.Png);

The problem is because you have not selected the active frame that you will create the thumbnail from.
I cannot verify it on my current machine, because I don't have the Windows API on it, but it's giving you the standard PDF thumbnail because in your code you have't specified which page to use for the thumbnail.
Try doing something like this:
Image image = new Image();
//Load image here
int frameindex = 1; // Page number you want to use for thumbnail
Guid guide = image.FrameDimensionsList[0];
FrameDimension fDimension = new FrameDimension(guide);
image.SelectActiveFrame(fDimension, frameindex);
//Then go on to extract your thumbnail

I was not able to get ExtraLargeBitmap to work for PDF files but all other sizes (Large, Medium, and Small) worked fine.
Dim MyShellFile As ShellFile = ShellFile.FromFilePath(fi.FullName)
Dim MyThumbNail As Image
MyShellFile.Thumbnail.FormatOption = ShellThumbnailFormatOption.ThumbnailOnly
MyThumbNail = MyShellFile.Thumbnail.LargeBitmap
Me.PictureBox2.Image = MyThumbNail

Re-encoding of Jpeg Image in binary column when saving

I know there are similar questions, but I have a question concerning the storage of images in a binary-column.
I have a small windows forms app that loads an image into a picturebox control from a sql compact db using Linq2SQL. The user can drag any image (jpg,bmp,gif) on a picturebox. On the DragDrop-Event the image is loaded into the picturebox.
When I save the record following code is executed to store the image of the picturebox control:
MemoryStream imgStream = new MemoryStream();
pictureBox1.Image.Save(imgStream, System.Drawing.Imaging.ImageFormat.Jpeg);
myTable.MyImage = imgStream.ToArray();
I have checked the size of the byte array and it didn't change after saving the record.
Is the image re-encoded every time the Save-Method is called? It would be maybe then better to check if the image has changed at all.

JPEG images are decoded as a function of their being displayed by .NET (or really just about anything). So, if you pull a JPEG out as a binary, put it in a PictureBox (which will convert it to a raster format to display), then take that now-uncompressed raster Image and recompress it, you MAY end up making changes to that image.
I would keep the original bytestream for the displayed Image somewhere behind the scenes, and write that back to the DB when the user saves the data. This will not only help preserve the integrity of the image, it will boost performance by reducing the need to recompress the image every time.

If this code is called when you call Save then yes, the PictureBox will "export" itself as a JPEG every time. Are you noticing a performance issue because of this? If you want to avoid it, set a flag on application load and when the drag/drop event occurs raise the flag signaling that the Save method should update the image data.

Screen Capture Feature Overrides

what i want to do is write an application in C# like "fraps" and other scren capture apps that when you press the "Print Screen" it saves the current screen as an image.
What i thought of is that
"i could create a background worker thread that checks the clipboard after x seconds and if there is an image, that is now in clipboard because of print screen click, it writes the clipboard contents to a jpeg or bitmap file" bu i lack the following knowledge
How will i know that there is an image in clipboard or some text or file
how to write that clipboard to an image file like how to convert that data into a JPEG (LZ-W format) or bitmap format etc.
Can anybody endow me with some knowledge or guide or help from C# coding prespective

The saving to a particular format is incredibly easy thanks to the Image class:
myImage.Save("someimage.bmp", System.Drawing.Imaging.ImageFormat.Bmp);
As far as checking the clipboard, well you can do this, but i think you might run into issues that you won't know whether the image came from a Print-Screen, or from a Ctrl-c that the user did. However you can easily check the clipboard:
if (Clipboard.ContainsImage())
myImage = Clipboard.GetImage();