How to fix Uncaught SecurityError: Failed to execute 'getImageData'?

Question

JavaScript

I connected this plugin to create watermarks for images on the fly: www.patrick-wied.at/static/watermarkjs/jq

but when calling
$(document).watermark();

The console outputs the following:
Uncaught SecurityError: Failed to execute 'getImageData' on 'CanvasRenderingContext2D': The canvas has been tainted by cross-origin data.

Tell me why this is happening.

Answer 1

The image must be from the same domain as the rest of the site.