For garmin GPS changing Opening Logo, the units (for any series) allow to change logo by simple steps, which following;
1. Select 'System', to enter the system setting menu;
2. Choose 'Display', then select 'Change...' for 'Splash Screen';
3. Select picture from unit internal storage or Memory Card;
4. Wait for reading picture, and wait for 3 sec after picture displaying, then choose 'yes' to confirm to change opening logo.
5. Restart your unit, then you find the logo changed.
Must be BMP file or jpg and go to settings and display and have your SD card inserted with the LOGOS wanted and the system will ask where to download from; ie Garmin device sortware of SD card.
Then it does from the SD card always and this way will be safe to do. Follow your instructions in the 660 manual to do it OK,