We're starting to hear some reports that Gmail has recently started re-writing image URLs to point to googleusercontent.com

For example, an image that originally pointed to:
http://mysite.com/i.jpg

Will look something like this:
https://ci3.googleusercontent.com/proxy/...#http://mysite.com/i.jpg

Reports are this is only affecting personal @gmail.com accounts, and not Google Apps / business domains.

This has the potential to affect open rates for Gmail by only tracking the first open, then caching the image on their own servers for subsequent opens. If they are caching images pre-open, there's also a potential for false positives for opens to result.

Are you seeing this issue? Do your Gmail stats look wacky?

Let us know what's going on, and we'll keep you updated with what we find as well.