I have a couple of questions about a photo gallery page that contains little more than an H1 (i.e. Photo Gallery), images (with good alt descriptions, of course), captions, and anchors. Apart from that, it's just the usual main nav, footer, and skip links.

Is it a good idea to add some off-screen content, just a brief description, that outlines the purpose of the page or informs users that the anchors will open images in a modal overlay?

Is there anything else that I should do to make the type of content clear?

I would say that the title makes it obvious, as does the anchor text that leads to this page, but I never like to assume. It's surely conceivable that screen reader users could visit this page, even if it is unintentionally.

Even though the modal overlay does not contain text, forms, or interactive content, should it have ARIA attributes? I have so far struggled to understand that part of the ARIA guidelines, so I only really know about the landmark roles in HTML (which I have already implemented).