How to implement the loading and processing of images?

Question

Google

For practice, php came up with the task of creating a service for loading and simple editing by the user, but I have no idea what libraries / functions to load for processing, applying watermarks and simple transformations with a picture.
So far, there is no knowledge that would help to choose the optimal functions\libraries\keys_for_search_in_google that are necessary to solve this problem.
What do you need to know for such a task?
More specific questions, how exactly to give php the picture that is uploaded?
UPD , solved. These libraries will help in editing the uploaded image: SimpleImage/PHPThumb, GD.

Answer 1

Grab the SimpleImage/PHPThumb ready made libraries
Now this is a very simplistic question.

Answer 2

PHP has a library for working with GD images: www.php.net/manual/en/ref.image.php

Answer 3

An excellent lib is Imagine .