From
http://www.microsoft.com/windowsxp/expertzone/newsgroups/faq/default.asp:
Q. Why can't I save .jpg, .gif or .png images in their original format
in Microsoft Internet Explorer?
A. Sometimes, if you right-click an image in Internet Explorer and
choose Save Picture As, the list of available types in the Save As dialog
box will not contain .jpg, .gif, or .png. It will either contain both .bmp
and .art, or only .bmp. Here are two procedures that may fix this problem.
To empty your Temporary Internet Files cache
1.. In Internet Explorer, click Tools, and then click Internet
Options.
2.. On the General tab, click Delete Files.
To turn off graphic compression in the AOL client
1.. Go to Preferences in AOL.
2.. Click Internet properties (or WWW in some versions).
3.. Click Web Graphics.
4.. Clear Never compress graphics (or Use compressed graphics in
some versions).
