How to change white to transparent?

Question

PHP

I have an image with black text and a white background. It is necessary to replace the white background with a transparent one in order to add a background from another image.

Answer 1

The simplest solution is to open the image with the same GD, go through the pixels and check if the pixel is white. But in this case it will work only with absolutely white color, and without transient translucency.

Answer 2

photoshop