Depending on the camera used, your photo material will have a certain format/ height-to-width ratio. A "normal" digital compact camera usually generates photos with a 4:3 format. A digital reflex camera will normally take photos with a 3:2 format. If you take photos out of a film, these could have a 16:9 Format.
Foto-Mosaik-Edda is set to work with a 4:3 format by default. In order to keep your photo tiles from being cropped in the photo mosaic picture (if you have used, for example, a DSLR) you can easily configure the photos in Foto-Mosaik-Edda. To do this, just open up the settings window in the software.