What Does "Alt text too long" Mean?
Images have an alt text that is longer than the recommended 125 characters. When this happens, the entire alt text will usually not be displayed for screen readers and not be taken into consideration by search engines.
A typical image tag will look like this:
<img src="bagel.jpg" alt="Authentic New York bagels on display in a Brooklyn deli">
The src attribute specifies the location of the file, while the alt attribute (also known as "alt text") is a short description of the content in the image. When the image links have an alt attribute with more than 125 characters, it will be classified as Alt text too long.
Why It's Important
If the alt text is longer than 125 characters, it may be truncated to this length when displayed on screen readers (typically used by the visually impaired) or search engines.
If you have important content here, it will likely get cut off. This is a very low priority issue so you may decide this is not worth the time to fix it, and it won't have a significant impact on your rankings or site.
How To Fix
Locate the <img> tag for each Image URL and rewrite the alt text, keeping it to 125 characters or less. If you really need to write a longer description, consider using the longdesc attribute which was created for this specific purpose.
Some other good principles to keep in mind when writing alt text:
Be descriptive. Don't just use one or two words to say what the image is of. Be specific and think of it as describing the image to someone who cannot see it.
Keep it to 125 characters or less. While 1-2 words are not descriptive enough in most cases, don't write a novel. Since screen readers generally only show the first 125 characters of an alt text, this is a good target for maximum length. Use the longdesc attribute for longer descriptions if needed.
Use keywords. This can help your image be found in image search or even help the page rank for targeted keywords, too.
Don't overdo it with keywords. Keyword stuffing is never a good idea.