How do I get better lines for an image in Osmo Masterpiece?

Press the purple filter button in the bottom middle of the screen (three lines and a circle). Drag the slider to change the number of lines. If these are still no good, press the droplet icon, which will give you completely different lines. Depending on the picture, these can be a lot better even if they are more difficult to draw. Lastly, if you just want the original image, press the icon on the far right.