Not sure if this is expected behavior - not finding any indication of changes made to this effect recently - but after receiving an email from my sister that there were no photo updates to a thread I linked her to today, I found that by logging out and trying to view any posts where "attachments" is used to include photos, there's no photos. Being a web developer geek, I immediately tried another browser (stock IE11 install in this case) and found the same behavior, and using the firefox inspector I can see no attempts to even include the images in the posts (no div with class "imageAttachment" in the markup), so it appears to be a server-side decision, not some weird js or mixed content snaffu.
Is this a new "feature" or a glitch in the matrix? If the forum is meant to behave this way ... well, I'll just say that choice might require some revisiting. So much valuable information is included in photos here on permies that it would be a shame to not have that available to people, especially with no indication that they even exist for visitors not logged in / without an account.