The most common image formats on PCs are BMP and TIFs, both of which
can be opened or inserted into documents by almost any program. These formats
print ok, but the larger you want the picture to be the more disk space
it takes, which is a drag when downloading.
WMF, CDR and AI files are completely different, as they are vector files. They don't take up alot of disk space compared with TIF and BMPs, and they come out equally crisp at any size, from thumbnail to full page. Unfortunately not all programs can open these files.