"Adding tags and metadata is almost a necessity too. High-end
cameras can usually shoot what are known as RAW images. These files
are the high-quality recorded data direct from the camera's sensor,
but this comes in a dazzling array of formats, so isn't a format as
such, but a term applied to a huge number of different and often
proprietary file types.
"Because cameras have limited resources, the JPEG images they
produce can often be improved upon in software on a computer. A
good photo app will accept the RAW data and convert it to a JPEG
file. The long-used utility, dcraw, is often employed to decode
these formats, and all the apps here use it or their own libraries
to decode RAW files, to varying success."