Thanks Nicholas and Jerry,
First, sorry for my stupid conclusion... Maybe too much wiskhy.
But the wrong modification I've found give a right effect on the scale of image.
My project is still on localhost, but I have made a demo site for you :
frang.fr/04-terrains-j03/
On the "Test1" item of Sobi2, you ca see the problem when the page is not loading on the "Photos" tab (if the page is loaded on this tab, everything's right).
On the "Documents" tab, you can download a joomlapack installer of the demo site, including all the code, template, and so on.
Thanks to analyse the problem.
Kinds regards
François