I spent part of last week recovering old photos that I had taken while in Europe. In the process, I learned an important lesson. Convert all photos to JPG or TIF, if they are not already in that form. The photos I had were in the Kodak Photo CD format, actually Pro Photo CD, which has become obsolete.
I could not load the photos, and I wanted to use them for a project I was using. My first attempt was to download the free program Irfanview. I had partial success and was able to retrieve my images; however, they were not at the highest resolution.
After this attempt, I ran a search on Google and learned that Adobe Photoshop had dropped support for Photo CD with the last several versions and it was not clear how to add support to the most recent CS5 version. After some hunting, I was able to locate a couple of old CDs, which allowed me to install and activate Photoshop CS1. Once I had Photoshop CS1 running under Windows 7, I had no problem retrieving my old photos.
Had I originally saved the photos as JPG or TIF files, I could have avoided this effort entirely. For this reason, I recommend converting all photo files to JPG or TIF. At this time, these file formats are the most common and consequently, most likely to survive.
All About Images Blog 
if i’m backing up my photos on CDs (from Costco or CMPhotocenter), are they .jpgs on those CDs?
Current CDs from most vendors, including Creative Memories, contain either JPG or TIF files. The difficulty is with earlier CDs that may contain files in different formats, with cameras that use proprietary RAW formats, and with some photo editing software that defaults to proprietary formats.
To verify the file type with Windows computers, use Windows Explorer. Go into the Tools Folder Option settings and uncheck the box next to “Hide extensions for known file types.” The file extension will then display along with the file name.
How do you convert them to JPG or TIF?
To convert files, either use a conversion utility such as Irfanview (see above) or the program that originally created the file or came with the camera. Most programs have the option to save a file in either TIF or JPG format, although the default may be a proprietary format.
Love this! What a great talent you have as a photographer!
Another free program for converting files in one format to another is XnView. Though there is considerable overlap with Infranview, each handles a few formats the other does not.