Well, first let me apologize for only answering your question half-way. Putting the screen shot on the clipboard was as far as I read. Sorry.
I hope I'm wrong, and if so that someone corrects me. I believe that the screen shot image needs to be saved into a program for that purpose, such as (but not exclusively) Paint or Photo Editor, in order to be saved as a jpg or bmp or gif.
Now, if instead of a screen shot, you wanted to copy a chart or some other Shape object, it would be much easier. But at the point of being on the clipboard, a screen shot is in limbo and so I believe it would need an object model that can be accessed through VBA. I looked through the Library just now and did not see an available reference for Paint or Editor. For applications that do have an object model, it should work, but I could not locate one.
There are alternatives but you might not like them. One is to paste the image into a Word document and save as html. But the image would not be as sharp or clear as a jpg.
I know you said you want VBA so I won't try to sway you away from that. If anyone knows of a way to do it, I'm sure they will chime in. And again, I hope I am corrected about the hurdle(s) necessary to accomplish what you want...I just don't know.
In case anyone else is curious about a non-VBA approach, in addition to Mr. Phantom's suggestion, I found a nice downloadable product for screen shots and the like at
www.hyperionics.com