This has bothered me approximately forever. I know the general outline
of the answer, namely apps find media files through some index that
the system updates, but to solve or work around it I need more detail
than that. I think the same happens with audio, it’s just that I hit
the problem with pictures this last time.
Where do you put them? Which gallery app? Which device? Which Android version?
Android 12, as up to date as the vendor (TCL) allows.
Here’s what I did: On my computer, I created a .zip file of one
directory with .jpg files. I sent this file with magic-wormhole
and I received it on the phone with the “wormhole” app from
f-droid, version 1.1.10. From there, I tapped “Open with” and
I selected the “Ghost Commander” app from f-droid, version
1.64.2b4. In Ghost, I unpacked the zip and copied the unpacked
folder into /storage/emulated/0/Pictures. So far so good: I can
see the .jpg files are there, right where I wanted them.
Now I open the “Gallery” app from f-droid, version 1.13.1.
(I think this is called “Fossify Gallery” in the f-droid store.)
The new files are nowhere to be seen, scrolling to the bottom
to see the oldest doesn’t help, scrolling up to refresh doesn’t help.
However, I can tap each in Ghost, one by one, select to “Open with” Gallery,
and then they appear. It should be obvious I don’t want to do this
if there are many files.
I am pretty sure what I need is some way to trigger the media index
refresh after the new files are in place. I think this happens
automatically if files are copied onto the phone over MTP, but
that has other disadvantages.