In many phones, when you take a selfie using your default camera, the picture come without mirroring and you may not have any option in settings. So for just mirroring your selfies, you don't have to download big photo editing apps.
Flip multiple images , Batch image flipping -PRO Feature
You can flip image Vertically and Horizontally
Also you can Rotate images.
Note: This app will not be able to process large images, since its not reducing image quality. So if you try to edit an image of large size, the app may not work.
The app keeps the quality of the image.
Added in-app purchase for removing ads
View your flipped images in gallery
Share image from other apps to flip image
Flip Image – Mirror Image (Rotate Images)