[Django]-How to pass an argument to a method on a template variable in Django?

I agree with the philosophy of separating logic from design, but there’s an exception. I am currently writing a get_image(height=xxx, width=xxx) method for a model. Clearly, it should be up to the template designer to decide the size of the image as the last stage. Though I suppose the correct thing to do is write a custom tag, but why restrict?

Here I wrote a hack to call a function and pass the arguments
http://www.sprklab.com/notes/13-passing-arguments-to-functions-in-django-template/