The pictures matte and glass are held tightly in place by clips 0n 3 sides. The clips go securely into grooves in the frame. 
Altho they come with both black and white pictures, I am using my own photos. 
The only thing they could have improved on is the thickness / quality of the matte. It’s very thin. The template for hanging the pictures is great to have. So helpful for getting pictures evenly spaced !!