With Sketch, the image imported onto the Board is directly vectorized.
1 - Sketch selection
In the toolbar, click on "add", then on "sketch".
2 - File selection
Select your file (JPG, PNG or GIF)
3 - Display sketch
The image has been converted into a vectorized sketch (= resizable to different scales without loss of quality).
4 - Sketch modification
The sketch color can be modified. To do this, select the sketch and change the color by clicking on the color dot.