Simple way to upload and crop in image on my website

First of all I'd like to say that I looked at similar posts without any success.

What I'm looking for is quite "simple", I'm looking for a way to upload and crop an image in browser. The thing is that I have to maintain the highest possible resolution. All plugins i've found so far only allow me to crop images at the size they are displayed on the website completely destroying the initial resolution.

I'm not a JS expert so my ability to implement/modify the code is limited ..

If you have a lead for me i'd be grateful ! thanks !!