Frame - is one of the many single photographic images in a motion picture. The individual frames are separated by frame lines. Normally, 24 frames are needed for one second of film.

Screenshot - is an image taken by the computer to record the visible items displayed on the monitor or another visual output device.

Footage - the raw, unedited material as it had been originally recorded by video camera, which usually must be edited to create a motion picture, video clip, television show or similar completed work.

source: Wikipedia