* * * Carbon pen or ballpoint pen. * * Write with a black marker with ink. Carbon or ballpoint pen ink can be well combined with paper, so long as it does not damage the paper, the words will not fall off.

* * * Oily pen. * * Oil-based pen ink works well in photos and won't fade.

Please note that the above are just some indelible choices. It is still necessary to keep the photos dry and away from light, because environmental factors such as illumination and humidity may also affect the durability of handwriting.