That depends on whether you occasionally scan your logs (or stats) for evidence of hotlinking -- people putting image links on their Websites that cause their visitors browsers to fetch the images from your server. If this is not a concern, then you might want to disable logging for image requests.
Also matters for things link hitcount (or bytecount) tracking. If you don't log those requests, you can't track them at all; you can't see which images are getting hit hard, and figuring out how much traffic you're pushing in a day becomes tricky (to say the least). If these aren't issues, then by all means, look into not logging. Me, I log every request, even on the sites where I need to roll/compress my logs multiple times per day to keep things running smoothly. =)