Scenario: Samsung Galaxy S5, on T-Mobile network, fully updated so far as I can tell. 32 GB memory card. Phone memory ("device") got full, mostly because of saved photos (mostly, documentation of work related events). I just moved all the photos in "device" memory (that is, the contents of "Phone/DCIM/Camera/") to my desktop computer. Remaining on the phone are a few images in "Phone/Download/" and the images on the memory card (a small "album", and a few hundred work-related images) all of which are also duly backed up on the desktop computer and on a removable external HDD belonging to the same. So now when I bring up "Gallery" on the phone I get one album, a small set of "Download" images, 448 pictures in "Images" - - and one apparently blank image (or image placeholder?) called "Picasa". It's been there for weeks and I cannot find or delete it. I do not use Picasa (preferring to manipulate my images myself <G>) but somebody did once send me a Picasa file, of which this is perhaps the now-empty remainder. How to get rid of it? I've spent quite a bit of time looking for anything labeled "Picasa" on the phone, without success. On the "Gallery" screen this appears as a plain neutral-gray square labeled "Picasa (1)" alongside "Download (12)" showing one of the images there, "Images (448)" showing one of the images there, and "Tepe Gawra (13)" showing one of the images in that album.
When I use "File Explorer" (on the desktop, Win 10 Pro 64 bit, version 1703) I see the Galaxy as an entry under "This Computer". The subfolder "Phone/DCIM/Camera" is empty (I just moved all the files there to the desktop computer under "Pictures"). The folder "Phone/Download/" has the 12 images displayed in the "Download" group above mentioned, plus several .pdf document files that do not display on that screen. The subfolder "Card/Images/" has a subfolder "Tepe Gawra" (that is the album of that name) and 448 photos in .jpg format. No trace of Picasa.(and they are all photos taken by myself with readily recognized content).
So how to get rid of that boring Picasa gray square?