Quickly set an image's background to transparent, just click the button and choose the image!

Explanation

The app replaces all pixels with the same color as the current background color (based on top left corner of the image), and sets them to transparent.

If that color occurs inside your image as well, then it will become transparent in the image. (If you want to avoid this, first fill the background with a color that doesn't show up in the image, like a bright pink, and only that portion will get erased.)