I have question for you

If you are trying to make this GIF application on a regular Form and you are using the Image control to show the different frames then the Image control already has transparency so I don't understand why you need to deal with the TransparentBlt API. If you are trying to do this on a User Control then you are not going to get any transparency at all using Image or Picture controls; it won't work even if you use the TransparentBlt API. The only way to get transparency on a User Control is to draw the pictures directly on the UC window. Is this what you are doing?