An image with no alt text contributes nothing to topical relevance and gets nothing from image search. One with alt="IMG_4821.jpg" isn't much better, it's technically present and functionally useless. TechySEO checks every image on your site for both problems, plus the file-size and dimension issues that quietly drag down your Core Web Vitals.
Alt text is the only way a search engine actually understands what's in an image. Skip it and the image contributes nothing to the page's topical relevance, and it's entirely absent from Google Images, which for a lot of sites is a real traffic channel they're leaving completely untapped. On a site with a few thousand images, that adds up to a meaningful gap, not a rounding error.
The performance side is just as concrete. An image over 100KB is a direct hit to your Largest Contentful Paint, which is one of the three Core Web Vitals Google actually measures for Page Experience. Skip the width and height attributes and the browser doesn't know how much space to reserve before the image loads, so the layout jumps around as it comes in. That's Cumulative Layout Shift, and it's one of the more user-visible technical problems a site can have.
All of this gets checked across the whole domain at once, not page by page, which is the only way it's realistic to fix on a site with more than a handful of images.
Relevance, performance, and accessibility, in the same pass.
Run the audit and find the missing alt text, the alt text that's just a filename, and the images quietly dragging down your LCP.
