You’ll need to create a Dockerfile that you’ll use to deploy to app platform in order to install imagemagick. If using an Ubuntu base image, the lines you would need in your Dockerfile would be similar to this:

RUN apt-get update && apt-get install -y build-essential libssl-dev libreadline-dev wget && apt-get clean
RUN apt-get install -y imagemagick libmagick++-dev libmagic-dev && apt-get clean