Here is and easy way to batch resize photos and share on at least android.
Some people prefer to avoid social misledia which is probably a good idea or want to reduce bandwidth or online storage use. Some mobile photo sharing apps or storage services will resize automatically but the gmail app does not.
I had several photos on my phone that I needed to email but they totaled about 21 MB even after I had cropped them so it got rejected by gmail. They didn’t need the full resolution so I was able to easily batch reduce by 75% and share. This resolution still allowed zooming in with decent clarity.
The app has other features as well. If you don’t need it to take photos you can deny permission to use camera and it will still allow resizing existing photos etc…
The first one I tried had been downloaded more times but didn’t support resizing more than one at a time.