On the help page, the site mentions "categories" that can theoretically be added by the users. I see no way to add categories? Or are categories simply albums?
Maybe this part should be rephrased.
Categories are actually special public albums listed on the home page (and not-found pages).
Every user can add photos to them, but the list of categories is not modifiable (you can inform me if you think that one is missing, though).
Adding photos to albums (and thus to categories) is a bit tedious in the current version : you have to copy the URL and paste it into a form accessible via a button under the list of images in the album page.
When creating an album, one is theoretically given the choice for limiting image input to <just oneself, from others with a review process, and from others automatically>. One is additionally also theoretically given the choice of limiting viewing access to the album by either <invitation only via a link, or everybody>. However, on the page where you create your new album I see only one pull-down set of choices "Approbation: private / request / automatic"
Oops. The viewing restriction was an initial feature that I removed because it was (to simplify) too buggy, but the text remained.
Also "Approbation" sounds self-explanatory to me, but perhaps there would be a better word to replace it.
Possible that the dictionary says that this word exists (with apparently the right meaning) but that in fact it is not commonly used.