Licensing issues and use restrictions, read here and here on their website.
[doublepost=1526319238][/doublepost]Be careful about sites like this, they will typically restrict the images to personal use.
For commercial use without these kinds of restrictions and licensing issues, it's best to pay for content through sites that have royalty-free or rights-managed options.
AND, also be aware that even royalty-free and rights-managed content have licensing limitations. Be sure to read about these things on the content suppliers' websites before making a purchase, so you know what is and isn't allowed.
