Try going to VersionTracker.com and search for GraphicConverter. On the Info page for it there's a dropdown menu that will let you select an older version of the application. The link to download it will be below and to the left of the menu, not the normal download link above. It's always for the latest version. This may let you get the older version that does not require a code.
While you're at VT do a search for image editor. You'll find a number of them, commercial, shareware and free, that might be of interest to you. Gimp is a very powerful editor, not unlike Photoshop, that's opensource. There's also Seashore that's based on Gimp. Lot's of possibilities.