Cant post to library

i have been trying on and off all day to post to library and it wount work, not because i think its down but the stupid screenshot format. I am pritty sure i have my mod in the .zip format (it looks like a folder with a zipper on it) but my cant get any grafics program on my computer to display in .jpg they will only display as file type .jpeg. to make it worse it only says that the file or pic format is wrong so i dont know witch to fix can someone tell me how i can fix it?