Undo Removes Background Image Src

[brittonk]

My canvas starts with the user's photo (like in snapchat)

When the undo button is clicked, it removes both the last sketch mark as well as the starting background of the canvas.

For undo to work as expected, had to set CSS background in addition to the first draw of the image. This isn't ideal because I feel like some devices may not display a css sized background in a container the same as the canvas initially draws it... but maybe :D