I have been hard at work on a Joomla! site, and was stumped for a while about why an image wasn't showing up. I copied it backwards and forwards, made sure I had the right folder, swore at the image for a while. None of these things seemed to work.
And then it dawned on me, like the sun struggling through frosty winter fog: permissions. Now, *nix permissions are something I would love to master but never really seem to find the time to sit down and learn properly.
The crux of the problem is that anyone but the owner had no permissions at all for the image. Which is bad news if you want the world to see your lovely button graphic. So, I changed it to Read Only for Groups and Others, and we all lived happily ever after.