"If I understood correctly, you have a site on dev1 in 1.7.8, you copied it to dev2 and then downgraded it to dev2?"
I wanted downgrade the kopie (in folder dev2) to the Version 1.7.7.
I made the copie to work on the copy (dev2) and not on the original (dev1).
"Going back to the images, when you inspect the code, the image source link is something like: /dev1/image.png?"
Yes, on the dev2-version I had a string "dev1" in the source-link. That was the reason, I thought that presta use absolut source-links insead of relative.
yours,
Daniel