It's possible to have URLs in Coppermine somehow close to this form "www.mygallery.com/category-name/album-name/name-of-particular-picture"? Thanks for answer!
No. You'd need to come up with some custom code, plus enforce unique naming and a strict gallery structure.
Do you think it would be helpful or rather useless (in terms of SEO)?
Probably helpful, but I'm not an SEO expert.
I am reading book about SEO which says that it's possible to that with Mod_rewrite in .htaccess? But I don't know if I can do it with Coppermine too. What do you think about it?
Refer to what I said before. You'd need to make a custom script. It's not easy.
I am not a programmer, so that's out of question for me :) But thanks :)