Many image file formats can include various meta data (often called EXIF), like the date of creation, and perhaps the date of modification. And these details might differ from (and might be more authentic than) the concise and technical file info indicated by the operating system.

Many software will reveal such 'deeper' information, so look for the File Infocommand under the File menu in Photoshop, or the Metadata panel in Bridge.

Below you see an example of the raw (unfiltered/unsorted) details of a photo. In the panel on the left you can get a much more comfortable view of all details.

Note: this information does not need to be valid ! Anyone who knows how to tweak this data (either by using simple editing tools or by directly hacking the file), can alter the information. So the data is useless as proof in legal situations.

Oorspronkelijk geplaatst op Quora: How can I know when a picture was taken?"