Using a graphics program I made a grid and square by square duplicated what I saw. It was tricky, because the sweater's yarn isn't smooth, so some times shapes weren't distinct. I learned something about creating the repeat too. That was a challenge.
Then I chose yarn from my collection that seemed to be a good match. It was fun to discover I had some of each color already on hand. I haven't swatched it yet, but the colors do inspire.