You could have the C++ dll return the handle to the image using the GDI+ Bitmap.GetHBitmap(). Your C# control could then get an IntPtr containing the handle to the bitmap and use Image.FromHBitmap() to get the image object back. Human beings were not meant to sit in little cubicles staring at computer screens all day, filling out useless forms and listening to eight different bosses drone on about about mission statements. -- Peter Gibbons

I don't think there is any way of identifying whether a file is an image file or not unless we know the datastructures used to save each type of the file. Images are just binary files. Graphic applications which support multiple image types know this. But such a component may not be available in the public domain. You may check GIMP project. But it will be a touch job.