iPhone app hotlinking images from our website

I have been going through this for quite somet开发者_开发百科ime. We have a running website with a lot of images and we have a huge iPhone usage. But is there any way we can differenciate between what iPhone users are browsing and what iPhone users are viewing from their apps? We are suspecting that a certain iPhone app is hotlinking images from our domain. How can I find them or at least prove it? Would the app have a certain User Agent I can trace ?

Please note that do not own the app and I can't view the source code. I'm only in control of the public server that hosts the images

If the app is using NSURLConnection to retrieve the images it should by default have the app name in the User-Agent header, though it may possibly be adjusted by the app to hide its traces. The User-Agent should be obvious from your logs, I'd expect.