What this check inspects
Shipwork parses every img tag on the page and reads src, alt, loading, width, height and the common lazy-load attributes data-src, data-lazy-src and data-original. It reports alt coverage as a percentage of images with meaningful alt text, treating an empty alt as an intentional decorative image rather than an omission. It flags images missing width or height, images whose declared size is above 2000 pixels on a side, and, for up to three of the largest or most suspicious images, sends a header-only probe to read the file size without downloading it. It also reports images served as PNG or JPEG, whether the first image is lazy loaded when it should not be, how many below-the-fold images are not lazy loaded, and images with only a data-src and no src fallback.
What a failure means
Images with no alt attribute at all are warnings, because a screen reader announces nothing and image search cannot read them. Missing width and height are warnings because they cause layout shift. A first image that is lazy loaded is a warning because it delays the most visible image. Oversized files and images that exist only behind data-src are warnings, since the first wastes bandwidth and the second renders nothing for a crawler without JavaScript. Legacy PNG and JPEG formats and below-the-fold images that are not lazy loaded are informational.
How to fix it
- Give every informative image a short, specific alt attribute, and use alt="" only for images that carry no meaning.
- Set width and height on every image so the browser reserves space before it loads.
- Re-export oversized images at the size they display, and serve WebP or AVIF where the platform supports it.
- Leave the first, above-the-fold image eager, and lazy load everything below the fold.
- Give lazy-loaded images a real src, not only a data-src, so crawlers and no-JavaScript clients see something.
A typical failure, worked through
The setupA store exports every product image at the maker full resolution and lazy loads the whole gallery, including the first image, from a data-src that a theme script swaps in on scroll.
What the check reportsThe check reports low alt coverage, oversized files on the large images, a first image that is lazy loaded, and images that load only from data-src with no src fallback.
The pointEach finding is one line of theme output away from a fix, and together they explain a slow largest paint and a gallery that image search cannot see.