Answer:
Montage
Step-by-step explanation:
This question is somewhat confusing, but I got it.
Assemblage can mean any combination of media within arts, so that can't be a specific definition for photos.
Collage can use multiple forms of art, including visuals, colors, etc. Additionally, collages can also occur in music, so that's not the definition
Mosaic is patterns or images made with small pieces of tile or stone, so this doesn't apply to photos.
So by definition, the combination of different photographic images is a montage, despite the fact montages can be made in a video format.