In older versions, Gallery used to insist on the NetPBM library (installation requirements). However, it now supports ImageMacick as well. During the installation/configuration script, the pre-screening reported that NetPBM was found (“All 12 files found”) on my host. So, when presented with the pull-down to choose between NetPBM and ImageMagic, I just went with that…
The rest of the installation seemed to go fine. I then went to upload some photos and I started getting errors (the mind-numbingly vague “Unable to make thumbnail(0)”, whee). So, I re-ran the configuration script and turned on debug-mode. Then, after trying to upload photos again, the debug-mode diagnostics reported that one of the NetPBM files couldn’t be found (I’m still not sure whether this was the fault of Gallery or a mistake on the part of my hosting provider).
Since the NetPBM files were shared among several domains on my host and out of my reach (permissions-wise), I decided to attempt to install the latest version of NetPBM on my own. So, I uploaded those files to my host, set their permissions (755) and re-ran the Gallery configuration script. I told it the location of these newly installed files, but I just couldn’t get Gallery to recognize them (yuck).
I was about ready to give up, but then I remembered that Gallery supported ImageMagick as well. Of course, the pre-screening script didn’t affirm the discovery of ImageMagick files, so I wasn’t even sure if they were installed. But, I tried it anyway — setting the image-library in the configuration-script to ImageMagick — and it just worked (whew).
Don’t get me wrong — Gallery is a great program. But, its installation seems to become a bit wonky if it veers off its best case scenario. And, the “installation instructions” (if you can call them that) were a bit terse. Some of the steps were on the level of asking a novice cook to “julienne a potato”. Sure, that may be straightforward to an experienced cook, but it would also be understandably tough if you don’t even know what julienne means.
(And, just to clarify, I don't consider myself an expert cook, nor did I know what julienne meant until I looked it up just now.)