There are a few things you need before starting to cartoonize a photo in Photoshop. First, you’ll need to create a new layer on your photo, and name it " Cartoon." Next, select the Rectangle tool and click on the top left corner of your Cartoon layer. Then, drag the rectangle down to the bottom right corner of your photo. Finally, use the Pencil tool to draw a line across the top of your Cartoon layer and release. Now, use the Brush tool to paint over any areas that have been drawn with the Pencil tool.