In doing experiments or studies that could relate to science questions, it is often necessary to save data for analysis. Often this data will in number, though many other things can also serve as data.
Data comes from observations, measuring, counting, etc. What is being observed measured or counted, etc could be anything. Sometimes the chance to get information passes quickly and some way, for instance, a photo, might serve to freeze a moment, to take information from an image/ photo rather than from the thing directly.
What might these photos be ? For instance, if one wanted to count the number of birds in a flock in flight, certainly a snapshot would make this simple compared with counting actual birds.This might be contrasted with a series of photos taken over months to note the slow growth of hair.