Resize images by PHP

[provotector]

Hi! I'm preparing a function that show pics inside the chat window when a user post a image link.

All goes OK, but I have a problem. When a user places a big pic, the server and entire chat freezes for a few minutes. This is normal, due to the big size of images.

I need a funciton, that recieves a url image link and resizes the image to return the link of resized image, and show the pic as <img src> in the chat window.

How can I do the image resize with PHP code??? Any help for this??

Thanks for all!! And best wishes.