It is straightforward to produce images from most molecular graphics packages, including RasMol and Mage (e.g. use RasMol's Export function on the menu, or the command write GIF <filename>). Annotations can be added to RasMol: label string displays the text string next to the currently selected atom(s).
More sophisticated labelling and other manipulations of image files will require drawing/painting software packages.
(The following are not necessarily all freeware/shareware)
The following URL maintained by Lance Ladic at the University of British Columbia Computer Science Department lists Freeware/Shareware Graphics Applications (miscellaneous graphics packages, not just painting/drawing)
Earlier browsers could only interpret GIF (Graphical Interchange Format, compressed) and XBM (bitmap) file types, but more recent versions can also understand JPEG files. JPEGs allow a degree of control over the image quality; of course better quality JPEG files are larger in terms of storage.
The following references are in the archives (Ohio State University) of the comp.compression newsgroup:
There are more useful links on references page.
where **** is the 4-letter code)
Last updated 15th Jan '97