Update...

I decided to completly redesign the user interface. The layout with the book was great but it took too much room and it was not dark enough

Now I come up with this awsome ui. This tree brings you clarity even if you have many photos in a single category. As you can see on the image it displays photos with no children attached to them all in a row (a tooltip tells you the name of the respective photo if you hover over it). When you have huge amounts of photos this can be a live-saver. This time I code the tree myself with the help of jquery rather then using the jquery plugin jstree. At the moment it can only expand categories (photos with children) by fetching the data via ajax but I will add multiselect and drag’n’drop to it!
And another big change. The system creates now the resized photos on the fly. I’ve created a php script which returns the resized photos. This reduces the overall loading time dramatically and grants counting the views. This doesn’t makes the system less secure because to access a resized photo you need its key which can look like this: 9729d7355da1da160e625725bd10d72e. No key, no photo. I do this with a standard modx connector but I have the following problem.
[Revolution] Use connector for frontend stuff I appreciate that if you can help me with this.
regards,
JB