This is the js my ISP (VodafoneFJ) injects into all web pages: https://gist.github.com/mark-up/5297830

It basically optimizes images and replaces all image alt text with text saying to hit CTRL+R to load full-versions of images.

I know that VodafoneUK and VodafoneAU do the same.

On the bright side, at least they respect the no-transform cache-control header directive.