O right i delete the orginal extention in the name and usually save them as .png. They are a .png file format because they keep the quality and reduce the bytes needed.
Try in on this smilie:
Here is the .png format (it was orginally a .gif)
Hobbes take ur avatar for example its an .jpeg i have saved it as a .png in a seocnd. (You can give it any extension you want even made up ones)
This shows what you normally see wen u r about 2 save it
This is what i do to save it as a .png (you can save it as a bmp, gif, anything yoy want.)
Here's is your avatar in a .png format:
Hope this helps