Is something illegible even if the words themselves are clearly written?

Say you have a photo of a piece of paper with printed words, but it's hard to read either because the words are too small, or the lighting is bad, or maybe the focus is not sharp, would you still call it "illegible"? We tend to associate "illegible" with words/letters that are hard to read because of the words/letters themselves being sloppy or poorly printed, but what if the words/letters themselves are clear but you can't read them because of your perspective? By definition it seems to work, but it never sounds right when I use it that way.

Yes, if it can't be read because you can't make out the words, no matter the reason, it is illegible. You already know that the definition indicates that something too small to be read is illegible. It's not just a technicality: people use "illegible" to mean that. Here are a few examples:

• It is printed on a single sheet of foolscap, and the writing is so small that it’s illegible. —The New Yorker

• If someone can’t easily read text from the back row, it is too small. It isn’t actually the pinnacle of cool design to make it illegible. —The more accurate guide to the future

• For most documents, body text should be around 12 points. Fonts at smaller sizes may be illegible for some audiences. —Accessibility at Penn State

And here's some for "legible" along the same lines, for good measure:

• Font sizes less than 16px are too small to be legible and require mobile visitors to “pinch to zoom” in order to read. —[SEO Audits] Document uses legible font sizes

• Make plots large enough to be legible, and size similar plots to be consistent. —Writing up Results

• Authors should provide a poster title using letters large enough to be legible at ~ 3 m (10 feet). The title will be displayed at the top of the mounting board and will contain the authors’ names and affiliations. —Poster guidelines – ANIMMA 2019