Hi, I have used a custom import.php file found here on the forum to limit the image file to a certain dimension (can't find original post, see .zip in attachment).
concrete > core > libraries > file > importer.php

It works on other website I build, but now I added it to a new website.. but when trying to upload a Image, it does not work (So image does not get uploaded and the loading icon keeps going.. nothing happens). Replacing the original

------ SOLVED ------
I had overwritten the original file instead of placing it in the correct place:
root > libraries > file > importer.php