Handy Magnifier (magnifying glass). The application designed specifically to be controlled by single hand. Very easy to use in the shop while in one hand you hold a label and the second hand controls the application.
Tap the screen once, which would focus the camera.
Press and hold the screen, which would lock / unlock the image. You can save a screenshot in this mode or view the image from a different angle.
Slide your finger across the screen up or down, to change the zoom.
Tap the screen twice that would turn on / off the back-light.
Please note some features may not work, depending on your hardware. Just uninstall the application in this case. We apologize for any inconvenience.
Since v1.1.0 we use ScaleImageView by Ishii Kenzo :https://github.com/matabii/scale-imageview-android
It's awesome and easy to use!