A somewhat brief guide to accessible images on intfic, because accessibility is not an afterthought and we have many blind forum members. (ETA: This is in markown mode, in the html mode you just click the image alt text to edit it).
Let’s say you upload a picture here. When it’s uploaded, by default it looks like this: 
To denote something an image in markdown, you put an exclamation point ! before a link. The stuff in brackets then becomes the image’s alt text. After the pipe | is the image dimensions. The stuff in parentheses is the link to the image.
The alt text is visible to sighted users in the dialog popup whenever you click on an image, and is read out to screenreaders when there’s keyboard focus on the image. But the default string of numbers is meaningless as alt text! You should get in the habit of replacing this with a useful alt text description–there’s guides on this everywhere, but I like this guide from WebAIM a lot.
But imo you should have it in that mode anyway, it’s so much easier to use! You can view alt text in the non-Markdown editor, but I haven’t found any way to add or edit it.
I’m testing it here, and I see the image but not the alt text. The image above does not preview and doesn’t show the alt text - possibly because it’s being shown at full size already? Hopefully it still reads out for screen-readers.
The slightly bigger second picture works. I also see in markdown mode you can click the pencil icon in preview to edit the alt-text, which defaults to the image name. Carousel-ifying these to make sure it works:
The alt text is nonetheless present (visible in page source / Firefox dev tools / Page Info). I don’t think browsers generally make the alt text available in the regular UI (unless the image fails to load). (Some websites choose to make the text provided for the alt attribute also visible by other means, such that users not using assistive features are likely to encounter it.)
Yeah, normally what you put in the first part of the brackets gets set as both the “title” and “alt” HTML properties for that image, and the title property is what shows up on hover, whereas for small images displayed at full size it seems to just set the “alt” property, which is not usually surfaced for people for whom the image is displayed. I guess anything past a certain size is treated as possibly not being displayed at full size, therefore details might not be immediately visible, therefore the alt text should also be shown on hover? But I’m just guessing.
