How do I turn on a picture preview when working on a puzzle?

You can use two types of puzzle previews when working on a puzzle:
1) On devices with a small screen the preview button sets the puzzle preview as a transparent background image. Tap on the Preview option to open it

2) On devices with a big screen two options are available:

- the preview image of the puzzle in a small window. You can zoom in/out the picture. Tap on the Picture option to open it

- the preview of a puzzle as a transparent background image