I finally found the solution, the trick is to first click here to add the image:
In the code:
import Poco from “commodetto/Poco”;
…
// load first bitmap of the ressources
let background = new Poco.PebbleBitmap(1);
…
// draw background picture
render.begin();
render.drawBitmap(background, 0, 0);
That’s it, bingo

