Same issue, replying to your comment: "the optional attribute href" means it's not a must for an img to have it, like it is to have attribute src. But if the img is a link that takes you to a different page or content, you must include it. The figcap even says "Még több fotó a galériában. Kattintson a képre!" which means "Even more photos in the gallery. Click on the image!", so omitting the link is obviously missing essential content.