After importing an image, it can be useful to reduce the opacity so it’s easier to see your lines when you sketch over it. Here's how to do it:
  1. Select your image.
  2. Tap the opacity button on the tool wheel. It should be the only thing there that isn’t grayed out, besides the undo button.
  3. Drag the opacity slider to where you want it to be, then tap anywhere on screen to deselect the image.
Alternatively, you can decrease the opacity of your image layer. To do this:
  1. Open the Layers menu and select the Image layer.
  2. Tap the layer again to bring up the layer’s popup.
  3. Slide your finger along the opacity slider to decrease the opacity.