Reflow (original question)

This is to answer Sarah's original query in the Reflow thread, and give my
take on it (others may differ). Since that thread is now all about AI, I'm
starting a new thread for this answer. It will probably help if any more
comments on AI are kept in the earlier thread "Re: Reflow".

First, this SC has an advisory technique specifically for images, Technique
C37:"Using CSS max-width and height to fit images". It basically says that
to avoid the need for a horizontal scroll bar at high zoom, we can limit
the size of the image to ensure it stays within the available window or
other container without scrolling - i.e. it doesn't zoom with the rest of
the content. I think that recommendation partially answers this question -
some images don't need to zoom to high levels. Those images should, I
believe, be treated as covered by the SC and not zoom to the point of
needing a scroll bar.

For most mages, like the example you quote of photos in a news article,
landscapes and townscapes for instance, or head shots of a person, that's
probably ok, people can still understand the picture, albeit at a smaller
size than if the image were zoomed with the other content. (On the other
hand, a particular image might show an important small object somewhere in
the scene, that would be lost to low vision users without zooming - that
could be an exception.)

But the SC specifically excepts mentions "images required for understanding
(such as maps and diagrams)". Maps and charts and graphs usually have a lot
of writing on them. To someone needing 400% or more zoom to read the
surrounding text content, keeping a graph image small, aka Technique C37,
would leave the text on the graph too small for them to read. Hence why the
SC classifies that kind of image as an exception to the SC, and it's ok to
zoom them beyond the viewport. The same would apply to an infographic with
lots of text in it; they usually fail SC1.4.5 "Images of Text", of course,
but if there was one that validly passed 1.4.5, then it would be an "image
required for understanding" that could be allowed to expand beyond the
viewport.

So, critically, whether an image is caught by the Reflow SC, or can be
excepted and allowed to zoom with a scroll bar, I think we have to decide
whether, and by how much, the image is an "image required for
understanding". That is often a subjective decision. Consider a head shot
of the prime minister, for instance, in a news report. Is that
informational? Not really, I would say, most people know what he looks like
and such a photo would probably just be there to add visual interest to the
report. But if the police published a similar head shot of a dangerous
criminal with a warning to people to keep clear of them (no, not the prime
minister!), that photo is highly important information so should be zoomed
along with the other content for people with low vision needing high zoom.
I hope this answers your query, and sorry for the delay in replying to your
second query.

BTW: I think the phrase used in the this SC and it's second Note,
"two-dimensional layout", is somewhat confusing here, and hard to
understand (and maybe why this question was asked). All images are by their
nature two-dimensional, but I think only some images are in scope of the
SC. You can't really say that a photo has "two-dimensional layout" in quite
the same way a data table has. No one laid it out, it's just what the
camera saw. A bit of clarification or re-wording to that Note might not
come amiss.