the screenshots i take are invalid formats

When I take a screenshot in the world editor or in game i go to use that image for a minimap or i got to crop or convert its format and it say invalid format or says this program has performed and illegal operation and will be shut down. If anyone can tell me what I am doing wrong it would be greatly appreciated.

Which program are you using?

I think it has to be in some other format than jpeg. I'm no expert but I think it should be blp. Might wanna ask this in map making or do a search.