Li vidas la reflekton antaŭ ol riveli la foton.

Yes:

• Li = he
• vid-as = see + present tense, so sees
• la = the
• reflekt-o-n = reflection + noun ending -o
  • direct-object ending -n
• antaŭ ol = before
• rivel-i = to reveal / to develop
• la fot-o-n = the photo + direct-object ending -n

One nice thing about Esperanto is that the endings tell you a lot:

• -o = noun
• -as = present tense
• -i = infinitive
• -n = direct object

Because -n marks the direct object in Esperanto.

In this sentence:

• li vidas la reflekton = he sees the reflection
• riveli la foton = to reveal/develop the photo

In both cases, the noun is the thing directly affected by the verb, so it takes -n.

This is one of the most important grammar points in Esperanto.

La is the definite article, like English the.

So:

• la reflekton = the reflection
• la foton = the photo

It suggests that these are specific things, not just any reflection or any photo.

Esperanto has la, but it does not have a separate word for English a or an. If you leave out la, the noun often becomes more general or indefinite.

By itself, ol is very often used in comparisons, meaning than.

But in antaŭ ol, it is part of a fixed expression meaning before when followed by a verb idea.

So:

• antaŭ ol riveli la foton = before revealing/developing the photo

This is very common in Esperanto. You should learn antaŭ ol as a set phrase.

Because when before is followed by a verb, Esperanto normally uses antaŭ ol.

So:

• antaŭ ol riveli la foton = before revealing the photo

But if before is followed by a noun, then plain antaŭ works:

• antaŭ la foto
• antaŭ la revelado de la foto

So a useful rule is:

• antaŭ + noun
• antaŭ ol + verb

Riveli is the infinitive, the basic verb form. In English, that is often the form with to, as in to reveal.

Esperanto infinitives end in -i, and there is no separate word like English to.

After antaŭ ol, Esperanto often uses an infinitive when the subject is understood:

• antaŭ ol riveli la foton = before revealing the photo

So this works a lot like English before doing something.

Yes, that is the most natural reading.

Because no new subject is named after antaŭ ol, the listener will normally assume that the same person, li, is doing both actions:

• he sees the reflection
• he reveals/develops the photo

If you want a different person, it is clearer to say so explicitly in a full clause.

No, Esperanto word order is fairly flexible, especially because -n helps show what the object is.

The given sentence is in a very normal order:

• subject + verb + object + time clause

But you could also say:

• Antaŭ ol riveli la foton, li vidas la reflekton.

That still means basically the same thing, but it puts more focus on the before revealing the photo part.

Yes, in a photography context it can.

Outside photography, riveli usually means to reveal, disclose, or make known. But in photographic usage, it can refer to revealing or developing an image.

So a learner might notice that this feels a little specialized. That is normal: the context matters.

In standard Esperanto, li normally means he, referring to a male person.

Historically, some people also used it more generally, but many speakers today prefer not to do that. So for a beginner, the safest understanding is simply:

• li = he

That is almost certainly how it should be read in this sentence.