If you want to combine your ZenLiner art with other pictures, or layer two ZenLiner pictures, there is a compositing window to automatically mask your picture and make creating such a picture an easy task.

Here a line art ZenLiner picture has been masked by ZenLiner.

And here it is, drag-dropped on another ZenLiner picture. If you don't drop it exactly right, just click the Undo and try again!

Of course you can also use a picture which has not been processed by ZenLiner, as well.

There are many tools in the Composite Window to help you in the creative process. You can manually mask, set the transparent color manually or automatically, or even combine pictures without masking.