This app and the compressed video app that they make are just amazing. They'll keep the screen running for you in the background. Keep the background processes running and it just gets done with no hassle and it keeps usable space on your phone open
It works great and is free. You have to watch an ad after you select the photos you want compressed and sometimes you can't close the ad without closing the whole app, but your photos will still have been compressed.
I love this app, the compression is good as the compressed output file sizes are small, of good quality, and are small fractions of their original size. The overwrite original file feature - replaces the larger original file with the smaller compressed file if you want to - is a game changer. Compresses photos & videos with the same app. You may also compress many files at once: I have compressed 70 photos at once; pretty sure more can be done, I just haven't tried. VERY USEFUL HIGHLY RECOMMEND.
Really like it! Fast and easy, no time-wasting nonsense. Got the Pro version for a few bucks to avoid ads, worth it. Update: still like it, use it for work all the time. But occasionaly shows the popup asking for a review, which as you can see I have already done. No biggie, just letting you know. Thanks!