Photo Mosaic vs Photo Collage
The two formats are constantly confused because both involve many photographs. The difference is structural: a collage arranges photos so each is seen separately; a mosaic arranges photos so that together they form a different, larger image. Everything else — effort, effect, best use — follows from that.
The Structural Difference
In a collage, the photos are the content: each is fully visible, individually framed, meant to be looked at one by one. In a mosaic, the photos are the material: each is small, chosen to match its position, and meant to disappear into the whole from a distance.
Put differently: a collage is read photo by photo. A mosaic is read twice — once as a single image, then again as many photos.

Side-by-Side Comparison
Reading distance — collage: one distance, up close. Mosaic: two distances, far and near.
Main image — collage: none; the arrangement is the design. Mosaic: one dominant image built from the tiles.
Number of photos — collage: typically under thirty. Mosaic: hundreds to tens of thousands.
Photo integrity — collage: each photo shown whole. Mosaic: each photo cropped to a cell and color-tuned to fit its region.
Production — collage: manual layout in any editor. Mosaic: requires matching software or a design service.
When to Choose a Collage
Choose a collage when each photo must be seen whole and unaltered — a year in review, a trip diary, a set of portraits — and when the number of photos is small enough that each deserves its own frame.
When to Choose a Mosaic
Choose a mosaic when you want one image with a second layer: a portrait that reveals a life, a logo built from a company’s history, a gift that rewards a second look. The larger the photo collection and the stronger the main subject, the better the mosaic.