Resize an image using Javascript or PHP [duplicate]

This question already has an answer here:

• Resize images and fit each image into the square mantaining aspect ratio (backend) 2 answers

I have been working with PHP for months and I really new to Javascript.

Before I start explaining the problem I am facing, let us observe this image:

When a user uploads a picture (the orange part represent the image uploaded), I want to resize it for it to get a specific height by just adding some colors (dark side on my image represent the added parts).

I Have been looking on the internet for the last 5hours but I have not found any article about this kind of projects.

Can anyone help me solve this issue ? Your help is really needed... Thanks in advance