Sketches referenced in this tutorial:
Image Prototype Demo
Only building diagrams of a complex system can sometimes be too abstract. It’s often helpful to add visual prototypes to your sketch, so you can track how the UI should look in a given state.
If you’ve already made screens in a visual design tool like Sketch or Photoshop, it’s easy to add them to Sketch.systems. You can attach a JPEG or PNG to a state by dragging-and-dropping from your file system.
Note: you must save a sketch before you can attach images and individual images cannot exceed 2MB in size.