Please help us re-photograph our images. We are very interested in finding out how the places, monuments, and surroundings have changed.

To help you with this task, we have developed a free, dedicated mobile phone app (currently iPhone only), which you can download from the home page. Just log in, upload our images and become a site detective.

You will need to register with Zooniverse to get a login name and password before you can use the mobile app.

How it works:

1. Log in using your Zooniverse login name and password

2. The app will ask you for your current location. Please allow, as this will enable the HEIR database to suggest images near to your location, which you may like to re-photograph.

3. Select an image to rephotograph. 

4. Once you are at the site, the app will help you overlay the old image with the new one you can see.

5. Match them up as best as you can, then press 'upload' if you are able to upload them straight away, or leave them on your camera roll to upload later.

Your re-photographed image will be sent back to our database together with a geo-location, allowing us to reconstruct where the old image was taken from. You may find that some of the sites have changed dramatically, and some may not be accessible at all anymore. All of this is important information - so please add a note in the comment section on the app.