Why are most thumbs in ZenPhoto square?

Random images, new images, etc.
Album thumbs, image thumbs (in most themes)

Aside from some old 6x6, or similar, square film cameras, I cannot think of any square "sources" (film or digital). I do not manually crop my images to be square. I shoot with a standard rectangle shaped sensor and used to shoot with standard rectangle shaped film.

I compose my photo to take advantage of the entire image, normally the subject is off center along the rule of thirds. When cropped into a square thumbnail any focal point that is off center and to the left or right is then not balanced or is cropped into pieces with only part of it visible.

ZenPhoto seems like it is made for photographers, yet the photos that we want to share in it are altered apparently for aesthetics.

Why?

Are aesthetics more important than the photos we are trying to display?

thumb size and shape is decided by the theme designer for whatever ascetics he wishes. Anyway, your observation is "off" as there are themes that use a multitude of shapes.

Find a theme that suits your needs or make one yourself. BTW, 35mm is not necessarily the standard anyway. so what "standard" do you suggest? 1:0.67 (35 mm and aps, but some varience by sensor), 1:0.75 (Cannon PowerShot cameras, but alo they vary) 1:0.58 (most cell phones)

The standard that I recommend is the source image. Keep the ratio and resize the long side to the dimension needed.

Some themes do have uncropped album and image thumbs, but the random images and new images features are normally square in those too.

There is no "standard" and not everyone has images with the same orientation. If you have a mixture of portrait and landscape formats a layout can look quite uneven. So cropped thumbs of the same size mostly look best from usability reasons (= more guidance for the eye so easier to scan)

Anyway, you can create your own custom theme or modify one and create even custom functions of those mentioned for everything using the sizes you like. There is most always a "get" variant for just getting the data you can format as you like.

Some themes let you also choose if cropped or not.

After checking most of the themes listed on this site, I have thought about creating my own. I am very good with HTML, good with CSS and fumble around in PHP.... it may be a lot of work for me.

Thank you for the feedback.

Creating a custom theme is the best to get what you want both layout and/or functionality wise. And it makes also your site more individual, too. And yes, a drawback is that making a good theme is quite some work.

Best is you read the theming tutorial and maybe use one of the existing ones as a starting point.

Follow-up question, in looking at doing my own theme...

It looking at the functions guide, I am curious about something.

Can I set either a horizontal or vertical size, and then have the thumbnail generated with the other dimension to match - as calculated by the dimensions of the image?

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Example:
Image 'A' is 800x600
Image 'B' is 1024x600

Thumbnail max width set to 200

Thumbnail for image 'A' is 200x150
Thumbnail for image 'B' is 200x117

The entire image, including the ratio of width vs. height is maintained.
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Basically, is it possible to "max" the one side and let the other fall where needed?

We have both a function to check for landscape format and also a set of maxspace functions.

there are "max size" functions that may be what you want.