What a pity that you cannot help me!
It's very strange:
All images are formatted in JPEG, various sizes!
And yet some (about 10%) are accepted as background, others are not (although the same size)!!
Maybe it's OPERA?
I tried but the zip file won't link.
the following message:
"ERROR: You do not have sufficient permission to perform this action!"
So far I thank you for your help and the associated time!