I've been digging in to this topic for the last few hours and though I have not been able to find an exact breakdown of how the GoPhoto.it extension works online, it appears to work like this:
* The GoPhoto.it extension is installed on someone's browser.
* That person then browses the Internet, viewing pages and photos.
* When the person finds a photo which they want to see better, they activate the extension and are shown an enlarged copy of the image on a site.
* In the process, a copy of the image is saved to the GoPhoto.it servers and is hotlinked back to the original image, building GoPhoto's image library (of a Yahoo and Google Image variety) and allowing for "add-ons" like effects to be applied to the images which have been captured.
This process would result in hits showing up in your stats and is why the images are appearing hotlinked on their site.