Questions & Answers about Al ver que hay un rayón, lo fotografío.
Al + infinitive often means when, upon, or as soon as someone does something.
So al ver que hay un rayón means something like:
- when I see that there is a scratch
- upon seeing that there is a scratch
It is a very common structure in Spanish:
- Al llegar, te llamo. = When I arrive, I call you / I’ll call you when I arrive.
- Al entrar, apagó la luz. = When he entered, he turned off the light.
It does not usually mean purpose here. It is expressing the moment in which the next action happens.
Because hay is used to say that something exists or there is / there are something.
- Hay un rayón. = There is a scratch.
By contrast, estar is used for location or condition, not for introducing something as existing in general.
You could say:
- Hay un rayón en la puerta. = There is a scratch on the door.
- El rayón está en la puerta. = The scratch is on the door.
So in your sentence, the speaker is first noticing the existence of a scratch, so hay is the natural choice.