A souvenir mark can look like an alteration
A passport is not a travel scrapbook: its pages are reserved for official visas and border-control markings. A novelty stamp from a tourist attraction is not an immigration record, but it still adds ink to the same document officials inspect. That can raise questions about whether the passport has been altered or damaged—especially if the stamp covers an existing mark, obscures text, or lands on a page intended for official use.
The risk is trouble at the wrong moment
A souvenir stamp does not automatically invalidate every passport, and border officials do not all respond identically. The practical problem is that you cannot control how a carrier or official will assess an unofficial mark. If they consider the document damaged or altered, you could face extra scrutiny, delays, or difficulty boarding or entering a country. Replacing a passport while traveling is far more consequential than missing a keepsake.
Keep the memory; protect the document
At places such as Machu Picchu, the stamp is meant as a memento, not as proof of a visit or an official entry stamp. Put it in a notebook, journal, or dedicated souvenir booklet instead. The simplest safeguard is to keep every unofficial mark out of your passport, leaving its pages clear for the people and systems that need to verify it.
