robchur wrote:

Check permissions. Apache needs to be able to write to the thumbnail
directories. Check that ImageMagick is set up right. Check that the path to
convert is correct in each configuration.

stanley wrote:

If the issue was permission, the mw.1.5.8 should produced error which is not.

stanley wrote:

After spending hours of trial and error, I found that the problem caused by
extra characters . " 2>&1"; on include/image.php. After removing that, image
thumbnailing is working again. I'm not a PHP expert, and I don't know the use of
this extra characters, but still this is a workaround to my problem. These
characters are not found on mw 1.5.8 (mw 1.5.8 works fine with image
thumbnailing, see initial description and comment #2).

modified include/image.php:

wfEscapeShellArg($thumbPath);
//wfEscapeShellArg($thumbPath) . " 2>&1";

2>&1 means "redirect standard error to standard output".
That's probably used to hide errors in apache logs.

Closing bug. Probably solution should be added (where?) to document it.

Bug was already closed in c5.