Hi piskello!
This is possible but not really an official and very clean way.
You can activate Project-Thumnail-Descriptions:
0_1504683559494_Bildschirmfoto 2017-09-06 um 09.38.08.png
Then you can write the project Category manually into the new field:
0_1504683618268_Bildschirmfoto 2017-09-06 um 09.39.49.png
Then comes the tricky part and you will need some basic knowledge of CSS and jQuery.
You need to hide the description and then only make it visible when you hover the image.
Do you know the basics of jQuery to do this?
Best!
Marius