You hire a designer to make your website. The designer creates a unique design complete with beautiful images. Six months later you get a letter from a stock-photo agency demanding thousands of dollars in order to settle claims they have against you for copyright infringement because your designer did not properly license the images he used.
A good contract with a designer will have them warranty that all images and code were created by them or properly licensed, and will require the design indemnify you for any claims of copyright infringement arising out of the work they performed.
If your designer isn’t willing to agree to those terms, find a different designer who will stand behind their work as original or properly licensed.