ImageMagick is just a manipulation tool. To upload an image, all you have to do is make sure you specify the enctype of the form to be multipart/form-data
Then make sure you have an input tag with the type of file. That will allow a user to browse for a file on their computer and upload it to your server. From there, verification and manipulation is up to you.
For a simple example please see Handling File Upload in the php manual.