As my first answer is more focused on technical details, I decided to open a second answer to give you some overview on my original "camerafinder" idea dubbed "C.A.T.T." (Camera Anti Theft Tool). Feel free to use my ideas, but please credit me proberly...

Contrary to stolencamerafinder, C.A.T.T. works on an opt-in-basis. As the owner of a camera, you sign up at the C.A.T.T. site, create a user profile and then register your cameras.

To do so, you are required to take a picture of some randomly generated QRCode displayed on the screen. Then you upload the unmodified photo to the C.A.T.T. site. When the upload is complete, the server reads the metadata of the photo and checks for an embedded serial number. It also tries to decode the QRCode from the picture and compares it against a stored hash. This is to prevent that somebody can register your camera by just uploading an arbitrary photo taken with that camera.

When your camera gets stolen, you login at the C.A.T.T. site and mark that device as stolen. To trace the stolen cameras, we planned a client-side exif serial number parser in javascript as mozilla greasemonkey script (similar to your chrome extension). It should only execute on flickr pages containing original images (thanks to greasemonkey's url pattern support) in order not to slow down the browser too much. The script would contact the C.A.T.T. server on a regular basis to fetch a list of stolen cam serials. If the serial of the currently displayed image shows a match, it would display an alert.

I saw that your chrome extension follows a similar approach (although it just seems to collect the serials). In your case I would leverage the extension with the W3C File Api (currently Firefox and Chrome), so that the user can also inspect locally stored photos and not just those embedded in webpages. Here is an interesting Mozilla demo on this.

As my first answer is more focused on technical details, I decided to open a second answer to give you some overview on my original "camerafinder" idea dubbed "C.A.T.T." (Camera Anti Theft Tool). Feel free to use my ideas, but please credit me proberly...

Contrary to stolencamerafinder, C.A.T.T. works on an opt-in-basis. As the owner of a camera, you sign up at the C.A.T.T. site, create a user profile and then register your cameras.

To do so, you are required to take a picture of some randomly generated QRCode displayed on the screen. Then you upload the unmodified photo to the C.A.T.T. site. When the upload is complete, the server reads the metadata of the photo and checks for an embedded serial number. It also tries to decode the QRCode from the picture and compares it against a stored hash. This is to prevent that somebody can register your camera by just uploading an arbitrary photo taken with that camera.

When your camera gets stolen, you login at the C.A.T.T. site and mark that device as stolen. To trace the stolen cameras, we planned a client-side exif serial number parser in javascript as mozilla greasemonkey script (similar to your chrome extension). It should only execute on flickr pages containing original images (thanks to greasemonkey's url pattern support) in order not to slow down the browser too much. The script would contact the C.A.T.T. server on a regular basis to fetch a list of stolen cam serials. If the serial of the currently displayed image shows a match, it would display an alert.

I saw that your chrome extension follows a similar approach (although it just seems to collect the serials). In your case I would leverage the extension with the W3C File Api (currently Firefox and Chrome), so that the user can also inspect locally stored photos and not just those embedded in webpages. This will surely increase your "serial number harvest", because no "man-in-the-middle" (flickr facebook etc) will strip out the exif data.

Here is an interesting Mozilla demo on Exif Extraction with the W3C File API.