Why do some images in Bridge appear as small icons while others are jpg images?
Sorry, we're going to need a lot more information before we can help you.
Where are you seeing these, in the Content Panel? If not there, where else?
What kind of files show up as icons (what is the suffix: jpg, CR2, tif, NIK, png)?
What is your OS (and what release)?
What version of Bridge are you using (and what release)?
Check in your file browser. Some images may not be supported in Bridge. Some images may not have embedded thumbnails. Also were these images that were opened in a different application and re-saved?
Like Gary indicated we need more info.