Hello Dropbox Forum!
Whenever I try uploading a .png to Dropbox it doesn't show up in the photos tab (dropbox.com/photos). At first I thought this was due to Dropbox not finding any date in the file (PNGs do lack exif support). However, after trying to both change the filename to the date (using format yyyy-mm-dd hh.mm.ss) and changing the creation/ modified date before uploading it still won't show up. PNG files appear to be supported as they show up when uploaded via the mobile image sync feature. I have tried uploading it to different directories on my Dropbox (including the camera uploads folder) using both the windows desktop client and the web client.
Kindly, a long time Dropbox user.