With the Unsplash plugin, and Sketch 52’s new Data Supplier feature, you can easily get beautiful images straight to your layers. Use it from the toolbar Data icon, from the contextual menu for any layer, or even for Overrides using the Inspector.
If you just need a random picture, choose the Random Photo option, and one of the images from the Unsplash Editorial collection will be selected for you and placed in your document. Do you need something more specific? Choose Search Photo…, enter a keyword, and the first result for it will be used. In both cases, the size of your layer will be used as a hint for the picture orientation, so you’ll always get great looking images that match your layout (no more vertical photos in your horizontal hero images!).