Alternatively (cause avk's answer seems too simple

):
All format-specific images descend from TGraphic so you can probably just create the proper graphic (TPortableNetworkGraphic or TJPEGImage) and use its
LoadFromClipboardFormat(), it there is such a format in the clipboard.
If that doesn't work (which is probable) just try the same trick with a compatible format (usually a TBitmap) or a TPicture.
Note that TClipboard has several methods that might help you to "divine" which is the format of the image it contains: FindPictureFormatID, HasPictureFormat, etc.