WEB - How to draw selection on Image

I want to implement a functionnality using a web Python framework (for now I start with Django but nothing is immutable) : Display the thumbnail of a PDF and draw rectangle to select a part of the image (Retrieve the position (X,Y) of the rectangle).

I search a lot, find some solutions using matplotlib (https://matplotlib.org/examples/widgets/rectangle_selector.html) but nothing on for a web version.

Any clues ?

Thanks in advance