Burst (by Shopify)

From the About us page:

Burst is a free stock photo site that is powered by Shopify. We have 1000’s of high quality and royalty-free images available and free to download. This includes a wide variety of images ready for you to choose from and create with (for more info, read our license page). We built this site to empower designers, developers, bloggers and entrepreneurs to create stunning websites and marketing campaigns.