Resizing a jpeg image

Good afternoon, I need to make the site so that the user uploads a picture and it is saved on the server in three versions: in the original size, medium size (somewhere 800×600) and small (somewhere 150×200), the image should save proportions.

Advise on how to implement this?


Answer 1, authority 100%

GD, you can fit in 50 lines…
But in principle, this is called zoom