SEO issue: links do not have descriptive text
Some SEO analyzers, like Google Pagespeed Insights could tell you, that your "links do not have descriptive text". This issue happens when you are using a non-textual layer, like an image layer with a link on it. "Descriptive text" means simply "text", and as an image is not a text, they are addressing this as an issue.
Or you can ignore this message, because it isn't an error, just an improvement suggestion. So your SEO won't be negatively affected by an image with a link on it. But the same link on a text would be better for search engines, as they would have more information about where it leads to.