Collages
This is a simple editing technique. The transparency mask is at the base of a good image composite collages are just a small fraction of the possibilities they open.
Read here more about Transparency.
Simple
Simply get items closer together without the risk of overlapping white backgrounds.
Editing is required and special PNG file format is used to put the final panel together.
Overlapping
First the background is completely removed from each photo and set as a transparency mask. This allows images to be the overlapped or at a minimum placed really close together in a collage.
Graphics
More often than not, graphics panels start with a collage.
You can see here more graphics examples.
