Profile Picture Preview

At 24px, Facebook's comment avatar is the smallest of the three sizes checked here, and the one most likely to actually matter — most people see your photo stacked in a busy comment thread, not framed alone at 170px on your Page itself. If a logo or face is still readable at that size, everything larger takes care of itself.

The 170px page-header size is what most visitors actually see first when landing on a profile or Page directly, so it's worth treating as the primary reference size here, with the two smaller sizes serving as a check for how the same photo holds up once it's scattered throughout comments and posts elsewhere.