Hello elad194,
Welcome to Apple Support Communities. We understand that you want to remove the video thumbnails in your iTunes library. We are happy to help.
Please try the steps here: Use iTunes to sync your iPhone, iPad, or iPod with your computer - Apple Support
"Sync or remove content using iTunes
- Open iTunes and connect your device to your computer with a USB cable.
- Click the device icon in the upper-left corner of the iTunes window. Learn what to do if you don't see the icon.
3. From the list under Settings on the left side of the iTunes window, click the type of content that you want to sync or remove.* To turn syncing on for a content type, select the checkbox next to Sync.
4. Select the checkbox next to each item that you want to sync.
5. Click the Apply button in the lower-right corner of the window. If syncing doesn't start automatically, click the Sync button."
These steps may help. Please let us know if you have further questions.
Take care.