Hi ! Thanks for your attention to this.
In the meanwhile, I must just admit that the module started to work when I disabled the Debug and the Dev mode in /ow_includes/config.php. It was in a test environment after all.
A similar mystery with the unexpected photo did not reoccur. If it does, I'll let you know after being sure what happened.
I discovered another issue that occurred when I used the secondary language interface (Dutch language). First, it didn't show me anything at all. Then I translated everything and it was still the same problem. Finally, I replaced the word "foto's" by "fotos" and then a bit later all pictures appeared. I'm not sure if an apostrophe really caused the problem.
I'm happy with the module now. It's looks better than the standard Photo view.
I'm going to change my review with this positive evolution.
With kind regards,
Alain.