The Crop Tool’s main job is to remove parts of a photo by cropping in tighter, but you can also use it to expand a canvas by dragging outside of the original image window to enlarge it. There’s also a handy Content-Aware feature in the Crop Tool options at the top. Toggle this on and, when cropping outside the original canvas, Photoshop will attempt to fill in the extra areas by generating new pixels. The results will depend on the complexity and size of the fill. If the backdrop is fairly simple, then the fill can be very successful – and even if it’s not perfect, it may take just a few moments spent cloning to finish off.