When you purchase a photo it is immediately delivered to your computer downloads. To find it, check your "downloads" folder. You will also have the photo in your "Purchases" page on the Twenty20 website.
To access your purchase history, click on your avatar (or username) in the top right corner of the navigation bar. Then select "Purchases" from the dropdown menu:
Your purchase history will be displayed and you can re-download any image you've previously licensed by clicking "Download". You can also export your purchase history by clicking "Export as CSV" in the top right corner: