This afternoon, I found out by pure chance the blog of an old friend. My reading stopped on two really interesting articles on HDR photos and centering photos correctly.
Thus I tried to find more informations on HDR photos and how to create them. This has lead me to an interesting Gimp script and I made some tests:
The photos 1, 2 and 3 are the original photos where we can see several different details, and the HDR photo is the one produced by the gimp script after some layers handling (because I have moved a little between the photos). Now I should try to make real photos like this.