Find some image hosting site like tinypic or imageshack
Find the screenshot
**Covert the screenshot from .bmp to something else (bmp are large files), (e.g. png or gif, not jpeg <-- low quality)
Upload new full size screenshot (.png is best I think) DO NOT CHANGE IMAGE SIZE/SCALE!!!!
Find link provided by picture hosting site that says "thumbnail link" or something. Should be in bbc code.
Paste code into post
Should see thumbnail to link of FULL SIZE screenshot
**If you don't know how to convert...
Easy way: MS Paint, open screenshot.bmp, SAVE AS, change file type. (remember where you saved it)
The Gimp, or any other image editing software can do the same. There are also free image file type converters everywhere (if you are lazy).
Smoke me a kipper, I'll be back for breakfast...