Make sure when you finish her conversation you go straight to the album. The Itch version of this game has a bug where if you talk with certain people after Umiko hides the pic it can glitch out.
There's an autosave each day, so reloading fixes this bug.
Can we a get which picture day 16 is supposed to be in? I went straight there after messaging with Umiko and I can not see it at all. It's the only one I've had actual trouble finding.
Edit: I've learnt that it's random. I found it, did some testing, and noticed it moved. XD Also, can confirm that it can fail to appear even if you go straight to the album after messaging Umiko.
