How does the passport washing machine work to ensure the security and integrity of travel documents?

The passport washing machine uses a special ink that is resistant to water and other liquids. This ink is used to print important information on the passport pages, such as the holder's personal details and travel history. When the passport is washed, the ink remains intact and readable, ensuring that the information on the document is not compromised. This helps to maintain the security and integrity of the travel document, making it difficult for unauthorized individuals to alter or tamper with the information.