Abstract: A photo notification system i comprises one or more mobile terminals, a data communications network, and a photo sharing platform. The photo sharing platform is configured to compare a received reference image (6.1), associated with a first user, with one or more stored images associated with other users. The platform identifies an object or scene of interest in the reference image (6.2), and compares the identified object or scene of interest with objects or scenes of interest in the one or more stored images (6.3) to identify common content having an appearance change (6.5). In such case, a notification message is sent to the first user referencing or comprising the stored image(s) having the identified changed appearance (6.7).