The suffix _full strongly suggests that this specific file is the available in a database, as opposed to a thumbnail ( _thumb ) or a low-resolution preview ( _low ). You will likely find files named this way in:

Right-click the file and select Properties (Windows) or Get Info (Mac) to see if there are copyright tags or authorship details.

The .jpg extension denotes a lossy compression format developed by the Joint Photographic Experts Group (JPEG) . It is the standard for digital photography due to its ability to maintain high image quality while significantly reducing file size.