// Original canvas

const canvas = new fabric.Canvas('canvas');

fabric.Image.fromURL('https://picsum.photos/500/500?image=0', function(oImg) {

    // scale image

  oImg.scale(0.5);

  canvas.add(oImg);

});

canvas.isDrawingMode = true;

const img = new Image();

img.onload = function() {

  var texturePatternBrush = new fabric.PatternBrush(canvas);

  // is it possible to also scale the image here?

  texturePatternBrush.source = img;

  // texturePatternBrush.scale(0.5);

  texturePatternBrush.width = 50;

  texturePatternBrush.height = 50;

  canvas.freeDrawingBrush = texturePatternBrush;

};

img.src = 'https://picsum.photos/500/500?image=0';

<canvas id="canvas" width="500" height="500" ></canvas>