Watermarked ballots

Committing fraud through photocopied or home-printed ballots would be highly difficult to do successfully. This is because each local election office has security measures in place to detect such malicious activity. While the specific measures vary, in accordance with state and local election laws and practices, such security measures include signature matching, information checks, barcodes, watermarks, and precise paper weights.

https://www.cisa.gov/rumorcontrol