Is it legal to download and use YouTube thumbnails? The short answer is: It depends on how you use them.

When it is usually okay:

• Reference & Inspiration: Downloading them to create a mood board for your own designs.
• News & Commentary: Using the thumbnail in a blog post discussing the video or the creator (Fair Use).
• Data Analysis: analyzing colors and text trends for research.

When it is NOT okay:

You cannot download another creator's thumbnail and upload it as your own for your video. This is a clear copyright violation and can lead to a copyright strike on your channel.

Disclaimer: This is not legal advice. When in doubt, ask the creator for permission.