Canvas cut marks

Question

I have this sample red image 16"x20", with 1.5" white padding and 4px black border. I created the border in Photoshop using Layer Style Stroke

The print will be on canvas, and the border is to be the cut line. The problem is that the 1.5" white squares in each corner need to be cut out, so that the 4 white sides can be folded down, something like this

  +---------+
  |         |
+-+         +-+  
|             |
|             |
|             |
+-+         +-+
  |         |
  +---------+

How can I create this type of border with Photoshop or Illustrator?

Answer 1

Illustrator: You can use compound shapes to get the desired shape. Take two rectangles that, when placed over each other help create the "shape" you're looking for, and then combine them using the Pathfinder tools into one shape. See http://helpx.adobe.com/illustrator/using/combining-objects.html for more details. Apply whatever stroke/fill/patterns you need.