Three very good, completely free high-definition image material websites. Designers need a lot of materials in their daily work, but good materials are often very expensive. A photo on 500px will sell for 50 to 500 US dollars depending on the size and authorization. So some designers will choose to use background pictures from some foreign websites. If you are found to use them for your own use, you will become a designer who steals pictures and plagiarizes in the eyes of others; if you are found to use them for commercial purposes, your company and you will face a lot of trouble, and even face lawsuits.