1. Upgrade to version 21.04 if you haven't already done so.
2. Start a new game in 2018.
3. Go to Advanced Tools on the Tools Menu.
4. Click 'Download Team Logos'.
This should take less than a minute.
When you're done, I recommend clicking "Download Player Photos". This will take a bit longer (5-10 minutes), but it will download and resize photos for about 4,000 players in the 2018 database.
All art is permanently saved to the "downloads" folder. You don't need to repeat these steps every time you start a new game.