Both is ideal, since not everyone who is legally blind has to use a screen reader. Some people have enough vision to scroll and read the size boosted text in apps, but they can't read images or images just don't have enough contrast. Alt text feels correct to me, but it doesn't show non-screen reader users that text. Captions do.

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I like to use both! I have some vision, but my phone doesn’t increase the font size on Instagram. Voice Over doesn’t always work for some reason when reading images (but is more convenient when it does), but always works when reading text. Thanks for checking with this community!

Alt text on Instagram is the better idea, that way the information is attached to the image rather than buried in a reply

Alt text all the way. Alt text is meant for descriptions with screen readers, and putting them in the caption just causes a bunch of clutter for blind people. Hope this helps!

I'm having trouble finding the alt text option on Instagram, so I always put written descriptions underneath. Does anyone here know where it is?