To highlight selected part of photo and rest will convert into large pixel image.
With Photo Pixel Tool, you can quickly pixelate unselected portion of an image to hide identities or to keep some things anonymous.

Pixelate images is quick and simple:-
1. Open app, select an image from gallery or camera.
2. Make your selection using rectangle, circle or free form tool.
3. When you're finished selecting the part of your image, tap GO.
4. You're all set to save and share