The answer is probably available to this, but I am not wording it correctly.

[AC Question]

I am running low on space, so am trying to free up some by deleting apps I don't use. My question: is the gallery app and photo app the same? As far as I can tell, all my pictures are in both. If they are duplicates, can I remove the contents in one app without affecting the other?

 

[ManiacJoe]

That will depend on what you mean by the gallery app and photo app.

Your photos are on your phone's "disk drive" in one or more folders. There is often a photo viewer app called "gallery". Lots of other photo viewing apps can be downloaded. Your photos are not "in" any app.

Your photos are taking up space on your phone's "drive", just like all the apps you have downloaded. If your phone allows you to use an SD card, the SD card is the perfect place to store photos, videos, and music.

 

[AlphaTango414]

If you are referring to the Google Photo app, it's content is cloud based storage.

Like mentioned above, your pictures are stored on your local memory. Mainly in the DCIM folder. Gallery and other picture apps populate itself but searching your memory for all supported formats set within a predetermined area.

Few options.
1. Use Google Photo to backup your pictures then delete the pictures off your device.
2. If applicable, move images to SD card via a file manager app.
3. Move images to an off device storage. Ie: PC, external hard drive, OTG USB, etc.