I installed zenPHOTO on my new site, and I could upload all my art, but I get an error trying to access any through the thumbnails. Here is an example.

192.168.1.101 - - [23/Jul/2015:01:49:56 -0700] "GET /zenphoto/index.php?album=all&image=Athena_Parthenos_Olympian_at_Olympus.jpg HTTP/1.1" 200 6169
[Thu Jul 23 01:49:57.443169 2015] [:error] [pid 11934:tid 139806260578048] [client 192.168.1.101:52827] PHP Warning: fopen(/srv/httpd/homesite/zenphoto/zp-data/debug.log): failed to open stream: Permission denied in /var/www/homesite/zenphoto/zp-core/functions-basic.php on line 1240, referer: http://davidchmelik.com/zenphoto/index.php?album=all&image=Athena_Parthenos_Olympian_at_Olympus.jpg
[Thu Jul 23 01:49:57.443272 2015] [:error] [pid 11934:tid 139806260578048] [client 192.168.1.101:52827] PHP Warning: imagejpeg(/srv/httpd/homesite/zenphoto/cache/all/Athena_Parthenos_Olympian_at_Olympus_595.jpg): failed to open stream: Permission denied in /var/www/homesite/zenphoto/zp-core/lib-GD.php on line 119, referer: http://davidchmelik.com/zenphoto/index.php?album=all&image=Athena_Parthenos_Olympian_at_Olympus.jpg
192.168.1.101 - - [23/Jul/2015:01:49:56 -0700] "GET /zenphoto/zp-core/i.php?a=all&i=Athena_Parthenos_Olympian_at_Olympus.jpg&s=595&cw=0&ch=0&q=85&wmk=%21&check=555628589e611bb5079041a73fde718ef4010aca HTTP/1.1" 302 -

Please see: http://www.zenphoto.org/news/permissions-for-zenphoto-files-and-folders

I have all my directories set to at least (usually more) the permissions stated on that page, as I had to do that in setup to get through that.

It depends largely on the server how strict you can set permissions. Also it depends if the server differs between FTP user and script user. Best contact your host.

I am my own host. Actually I made this post after having the problem in my 'language error' post, and reinstalling from setup.php. I think before that, I could access images, then not. I might try a reinstall from scratch, or maybe will need some paid support, but I am wondering how much that costs, for GNU/Linux. Thanks for answering stuff about this question so far.

Did you take a look at the folders to see which owner they have and what rights?
If those differ on those that work and those that don't, you might get a clue. I encountered servers that either allow access via FTP or via a script like Zenphoto. But not both. That means you have to switch rights frequently.

Since I am on our paid support page in advance that I personally cannot really help with server configuration itself as I don't setup my own servers at all.

Anyway, a reinstall from scratch made it work again, as it has before, so there is something with doing a reinstall with setup.php. Yes, I looked at the folders: when I said the permissions are what they were set to from setup, I meant I also verified. The same owner owns the directory for the site zenphoto is in, and all files/directories within. I do not quite know what you mean about servers, but I am pretty sure not all servers are like that. Ok, well I hope in the future people will be able to help people set up their server to make zenphoto work right.

I do not quite know what you mean about servers, but I am pretty sure not all servers are like that.

No of course gladly not all servers are like that. But I encountered hosts with that setup. And as said I personally just let hosts do the server stuff.

Zenphoto is aimed at users with shared hosting which is where I mostly isntall and use it. I never encountered such issues (except the rare weird server as above).

But glad you got it working again. Sorry, that I can't help more.