content/image-alt
Reports an image without alternative text: a Markdown image with no text between its brackets, as in , and an HTML <img> element without an alt attribute. Screen readers read the text in place of the image, and browsers show it when the image does not load.
Problem rule, reported only. Presets: recommended (warn). Dialects: all. Options: none.
Reported:
<img src="sales-by-month.png" width="400">Not reported:
<img src="sales-by-month.png" alt="Sales by month, rising from March">
<img src="divider.png" alt="">Edge cases and advanced usage
Details: Markdown text that is only blank space counts as none. An HTML image with alt="" is accepted: HTML marks a decorative image, which screen readers skip, with an empty alt, and the attribute is written on purpose. Markdown has no such mark, because  is also what an image looks like when its text was forgotten, so blank Markdown text is reported. Write a decorative image as <img src="divider.png" alt="">.
An HTML image hidden from assistive technology with aria-hidden="true", or from everyone with hidden, inert, or a style such as display: none, is accepted, and so is one inside an element hidden so.
Not checked: HTML images that renderers do not certainly show: those inside <template>, <video>, <audio>, <object>, <canvas>, <select>, <datalist>, <dialog>, <svg>, or <math>, or in comments or raw-text elements such as <textarea>. HTML images are found where content/html-element finds elements: not after HTML whose reading is uncertain, and not in footnote definitions that no reference uses. A report there could be about an image that readers never see.
No HTML image is checked after an end tag that a browser may ignore while an element that hides is open. A browser ignores the end tag of an element opened outside a table, a <select>, or a <template>, or outside a paragraph, list item, or table cell of the Markdown, and a start tag such as <li> can close a <p> before its end tag. In <div hidden><table></div><img src="x">, the image stays inside the hidden <div>. An end tag that closes the innermost open element, or that comes while nothing hides, does not stop the check. Nor is an HTML image checked after an <html>, <head>, or <body> tag: whether such a tag and its attributes apply depends on how the page embeds the rendered HTML.
Dialect notes
On GitHub: the sanitizer removes aria-hidden, hidden, inert, and style and keeps the image, so an image hidden only by them is reported.
In Obsidian: a size after |, as in , is not text, and embeds such as ![[chart.png]] are not reported, because they have no place for text.
In VitePress: only inline HTML images are checked, because HTML blocks are opaque areas. An image with Vue's attributes, such as :alt, v-bind, or v-if, or inside a component or an element with them, is not checked, because Vue decides what they show.