Traditional Culture Encyclopedia - Photography and portraiture - What do the numbers and letters behind the old photos mean?

What do the numbers and letters behind the old photos mean?

The numbers and letters behind the old photo indicate the number of this photo and the coding of darkroom technology. Among them, the number indicates the shooting date and sometimes the photo size; Letters indicate the washing process, including the type of washing liquid, washing time, developer, fixer, etc. These numbers and letters can help photographers track the process and history of photos, and sometimes help repair damaged photos.