3672 x 4896 px jpg images are not getting sized/displayed in Zenphoto album. 4896 x 3672 (landscape) are displayed fine.
Absolute jpg file size is not the problem, since larger jpg files are displayed correctly. I read the troubleshooting posts display problems with large image files. Debug information didn't reveal any error in the image. Tried switching to Image Magick engine, but that caused a whole lot of problems (caused multiple setup invocations and a bunch of errors), and was very slow, although some of the previously erroneous images were properly sized/displayed--switched back to GD. Can I set script maximum memory to higher than 128M in php.ini? Thanks for any suggestions.

I found a solution by myself.
Create a php.ini in the zp-core directory.
Add the line:
memory_limit = 256M;
This must be a very common problem in today's world of larger image sizes. Seems like this or another solution should be well-documented somewhere. Why not just add a memory variable in options-image to increase the php memory_limit?

Sorry, if your images are too big to be processed dimensionwise (as noted on the trouble shooting) there are only two options
a) Use smaller images
b) Provide more memory

Since b) will not be possible for most normal users not running their own server but shared hosts a) is the best option.

Sorry, acrylian, but I find your response particularly irritating, and customer unfriendly. Newer cameras are producing increasingly larger, not smaller images, and your solution is to stick your head in the sand and dump the problem back in your customers' lap. If I were a new Zenphoto user, uploaded a set of pictures, and found that all of the portrait mode pictures wouldn't display, I'd quickly jettison Zenphoto in favor of a tool that works properly on larger images. Requiring users to resize pictures just so that they can work with Zenphoto is not an acceptable workaround.

You underestimate the numbers of customers who can change the php memory_limit. I'm running zenphoto in a Bluehost shared server environment, as I'm sure great numbers of your other customers are doing, and my suggested fix above works. Why not at least publish an app note for people who are using Zenphoto in similar environments, with a disclaimer that it might not work for every user? To do otherwise is to show a profound lack of respect for your customer's time and energy when using Zenphoto.

First, Zenphoto has no "customers". We are not selling anything ;-)

Second, this is a server limitation of the graphics libaries and has nothing to do with "sticking the head in the sand". If your images are too big for your server raising the memory is a way to go.
If you can great. If you can't you need to upgrade your server or use smaller images.

All shared hosts I know don't allow changing the php memory (mine for example has 128 MB) so this is your only option unless you upgrade your webhost package to bigger packages. That are those the "normal user" normally does not have and if he probably knows like you how to raise the memory.

We currently set 96MB or more exactly we try to do that. We can raise that default value but again if the server does not allow it it does not help. It might even report a false value on the Zenphoto backend (which is noted there).

Also documented here btw:
http://www.zenphoto.org/news/problems-with-albums-and-images