Modifico la foto prima di condividerla.

Because Italian usually drops subject pronouns when they are not needed.

The verb modifico already tells you the subject is I, because it is the first person singular form of modificare.

So:

• Modifico la foto = I edit the photo
• Io modifico la foto also works, but io is usually added only for emphasis, contrast, or clarity.

For example:

• Io modifico la foto, tu la condividi. = I edit the photo, you share it.

Modifico is the present indicative, first person singular of modificare.

That means it can translate as:

• I modify
• I am modifying
• sometimes even I will modify, depending on context

In everyday Italian, the present tense is often used more broadly than in English.

That is a very common question.

Even though foto ends in -o, it is feminine:

• la foto
• una foto

This is because foto is a shortened form of fotografia, which is feminine:

• la fotografia
• shortened to la foto

So the gender stays feminine even in the shortened form.

Italian uses articles very often, especially with specific nouns.

Here, la foto means the photo, referring to a specific photo. In Italian, leaving out the article here would usually sound unnatural.

So:

• Modifico la foto = I edit the photo
• Modifico foto is not the normal way to say it in standard Italian

Prima di means before when it is followed by an infinitive.

So:

• prima di condividerla = before sharing it

This structure is very common:

• prima di partire = before leaving
• prima di mangiare = before eating
• prima di dormire = before sleeping

Because in Italian, prima di + infinitive is used when the subject of both actions is the same.

In this sentence, the same person does both things:

1. modifico la foto
2. condividerla

So Italian uses:

• prima di + infinitive

If the subject changes, Italian usually uses a different structure:

• prima che + subjunctive

For example:

• Modifico la foto prima di condividerla.
  = I edit the photo before sharing it.
  same subject: I

• Modifico la foto prima che tu la condivida.
  = I edit the photo before you share it.
  different subject: I / you

Because condividerla is made of:

• condividere = to share
• la = it

When an object pronoun is attached to an infinitive, it joins onto the end of the verb:

• condividere + la → condividerla

Also, the final -e of the infinitive drops before the pronoun:

• condividere → condivider-
• condivider- + la → condividerla

This is a standard pattern in Italian:

• farlo = to do it
• vederla = to see her / to see it
• mangiarlo = to eat it

The -la is a direct object pronoun meaning it, and it refers to la foto.

Since foto is feminine singular, the pronoun is la.

So:

• la foto → la
• condividerla = to share it

If the noun were masculine singular, the pronoun would be lo:

• il file → condividerlo = to share it

With a conjugated verb, object pronouns usually go before the verb:

• La condivido. = I share it.

But with an infinitive, the pronoun is often attached to the end:

• condividerla = to share it

In this sentence, after prima di, the verb is in the infinitive, so the attached form is the normal one.

No, that would not be correct.

If you use prima che, Italian normally requires the subjunctive, not the indicative.

So:

• prima di condividerla = correct, same subject
• prima che la condivida = correct, usually different subject or a more explicit clause
• prima che la condivido = incorrect

It can depend on context, because the Italian present tense is flexible.

Modifico la foto prima di condividerla can mean:

• I edit the photo before sharing it
• I’m editing the photo before sharing it
• I edit photos before sharing them if understood as a habit
• sometimes even I’ll edit the photo before sharing it

Without more context, the sentence is simply in the present tense, and Italian lets context determine the exact time nuance more than English often does.