The photos on your old iPod may be the last copy you have if you have lost your Mac. These photos are normally synchronized to you iPod by iTunes in a resolution suitable for the iPod and for viewing on TV. On the iPod they are stored in the ithmb format which is designed for use on the iPod only.
Fortunately you can copy the ithmb files from your iPod to your (new) Mac and use File Jucier to extract the images inside.
File Jucier convert the images inside the ithmb files to TIFF to preserve all the information from the ithmb files in a lossless manner.
The ithmb files are compressed using 16 bits per pixel in YUV format for television and they are therefore a bit smaller than the converted TIFF files.
The name ithmb is shorthand for thumbnail images, photos intended to be compact. The size of your thumbnail. Fast browsing in an iPod was the goal.
The largest of the ithmb files on the iPod, "F1019_X.ithmb" on the iPod Photo (X is a number), can be converted to TIFF by File Juicer. They contain the same images as you can find in the iPod's Photo cache folder. They are small copies of your original images - 720 x 480 pixels.
Newer iPods may put the best images in F1023 or F1024. On the iPhone the best images (640x480) are in the F3008_1.ithmb, F3008_2.ithmb ... files.
File Juicer can also extract the TIFF from the smaller ithmb files with the sizes: 176 x 220 pixels, 130 x 88 and 41 x 30 pixels. Usually you will only be interested in the images you can extract from the largest ithmb files.
The iPod can automatically synchronize the full resolution images too, although it is not turned on by default. You may be reading this page because you have lost your Mac and your iPod is the last place you have your images. After you have recovered your ithmb files you can turn this checkbox on.
Screen Shot of the iTunes preference.