Delete photos from iPhone

I wasn't able to delete photo's from my iPhone, even after searching and trying all the suggestions.

Then I read that I could only do it from the original computer which synchronized them.

As I didn't have that iMac anymore, that suggestion brought me the idea of another solution.

I put some photo's in a folder on my new Mac, and synchronized not from the photo app but from this other folder. Then all my photo's disappeared and I could delete the new photo's with another empty sync.

Finally I managed to re-sync the wanted albums by choosing to sync from the photo app again.

Hope that this serves others too.