Obsolete file formats
I got a bit of a shock last night while pulling the last bits of my digital image collection into a Photoshop Elements catalog. PS Elements lets you browse to a location on disk and pull in all the image files it finds, after which you organise them as appropriate. So, I dropped a load of images into a folder and pointed PS Elements at it. It didn't find any image files it understood. What? Why not? These were images from a PhotoCD I had made years ago, and the PS Elements organiser doesn't understand the PhotoCD file format, apparently. Fortunately, the editor itself does understand the format so a batch conversion soon dealt with the problem, but it seems the writing is on the wall for the PhotoCD file format.
The morale of this story? Don't write stuff to CDs and assume that as long as you have a working CD drive you'll be able to read the contents. Periodically check that the files on your archive CDs can still be read by your current software of choice. And even if they can, keep a copy in a different format just to make sure.
One day, jpegs will go out of fashion…