Trying to find the best out of a series of 15 photos shot in sequence? This app shows two photos on the screen in order to compare them. Zooming and panning is synchronized, so focus and composition can easily be compared.
The best photos can be selected, and the selection eventually shared. Alternatively, all photos which were NOT selected can be deleted from the device, freeing up space while keeping the best photos.

FIRST STEP - SELECT WHICH IMAGES TO COMPARE
What set of images do you want to compare? Choose from:

- An image folder
- A 'date taken'

SECOND STEP - CHOOSE STARTING POINT
- Choose sorting options from the action menu. When transferring images from a camera to the phone, some apps will create a wrong 'date taken' timestamp. In such cases, use the 'Sort using filenames' option
- Select an image as a starting point
- If you want to start with two specific image, long-press the first one, then select the second one

THIRD STEP - COMPARE
- Zoom / pan will synchronize between both images
- Disable the zoom / pan synchronization by toggling the button in the middle between the two images
- Reset both images to full view by clicking on the "center focus" button
- Option to show/hide EXIF data in the action menu
- Option to show light/dark image selection checkboxes in the action menu

Once the relevant images have been selected, choose "Show selection" from the action menu.

FOURTH STEP - ACTION
- Take an Android 'share' action on the selected images. Beware that more targets are available if only one image is selected.
- Invert your selection
- Delete the selected images
- Delete all the NOT selected images (depending on your selection in step 1, either in the selected folder,
or from the selected 'date taken').

A word about deleting images: This will really, physically, delete the files. They're gone afterwards.
BE CAREFUL TO NOT DELETE ALL YOUR PHOTOS!

ABOUT
I use the app regularly to decide which photos to post to https://www.instagram.com/simonniederberger/.

Open source at https://github.com/sniederb/photocompare