After me changing it (from Default) to -Image- it worked for the project detail pages. I also read that it is best to keep the DEFAULT but for now ill stick with IMAGE because I’m done with the missing images. 
Also, the second part of the problem (the missing images on the project overview page is solved bu changing the code into <a href="[[~[[+id]]]]">[[!+tv.pr-img]]</a>
Thank you all for being such a nice community and to put up with all my questions.
