When you're happy with the size and position, press Return. In the Layers palette on the right, Layer 1 is selected, representing the image you added. At the top of the palette, its mode is set to Normal. We clicked this and switched it to Lighten. If you were overlaying an image where the salient details were dark rather than bright, Multiply would be the option to pick, but it's worth trying each blending mode to see which works best.