Cette photo peut servir de preuve si le colis arrive en retard.

Because photo is a feminine singular noun.

French demonstratives agree with the noun:

• ce for masculine singular
• cet for masculine singular before a vowel sound
• cette for feminine singular
• ces for plural

So:

• ce colis = this package
• cette photo = this photo

Even though photo ends in -o, it is still feminine.

Yes. Photo is feminine: une photo.

It is also a shortened form of photographie, which is feminine too. So the gender stays feminine:

• une photographie
• une photo

That is why the sentence says cette photo.

Literally, it means can serve as proof.

Breakdown:

• peut = can / may
• servir = to serve
• de preuve = as proof / as evidence

So servir de + noun often means to serve as + noun:

• servir de preuve = to serve as proof
• servir d’exemple = to serve as an example
• servir d’aide = to serve as help

In natural English, this sentence could also be understood as:

• This photo can be used as evidence
• This photo can serve as proof

In French, the normal pattern is servir de + noun when something functions as something else.

So:

• servir de preuve = to serve as proof
• servir de guide = to serve as a guide

Using comme here is not the usual standard phrasing. A French learner should remember servir de as a set pattern.

Because after servir de, French usually uses de + noun directly, without an article, when talking about the role or function of something.

So:

• servir de preuve
• servir d’exemple
• servir de modèle

This is similar to saying something serves as something, rather than referring to one specific proof.

Because after si meaning if, French commonly uses the present tense for a real or possible condition.

So:

• si le colis arrive en retard = if the package arrives late

This does not mean only present-time lateness. It can refer to a future possibility too.

A very important rule: French normally does not use the future tense right after si in this kind of sentence.

So French says:

• Si le colis arrive en retard, cette photo peut servir de preuve.

Not:

• Si le colis arrivera en retard... ❌

Le colis suggests a specific package that both speaker and listener already know about.

So this sentence sounds like it refers to a particular delivery:

• the package

If you said un colis, it would sound more general:

• a package

Both are possible in other contexts, but le colis is more natural if you are talking about one known parcel in a complaint, delivery issue, or tracking situation.

Because arriver en retard focuses on the package showing up late.

• arriver en retard = to arrive late
• être en retard = to be late

For a package, arriver en retard is often more precise, because the issue is the delivery happening later than expected.

Compare:

• Le colis arrive en retard. = The package arrives late / is delivered late.
• Le colis est en retard. = The package is late.

Both can work, but arrive en retard emphasizes the act of arrival.

Yes. French allows both orders.

You can say:

• Cette photo peut servir de preuve si le colis arrive en retard.
• Si le colis arrive en retard, cette photo peut servir de preuve.

They mean the same thing. The difference is mainly one of emphasis or style.

If the si clause comes first, French usually adds a comma:

• Si le colis arrive en retard, ...

Peut is pronounced roughly like puh with rounded lips: /pø/.

The final t is silent, which is very common in French word endings.

So:

• peut sounds the same as peu in normal speech
• the spelling is different because peut is the verb form from pouvoir

Here:

• peut = he/she/it can or can with a singular subject
• Subject: Cette photo
• So: Cette photo peut... = This photo can...

Peut is the 3rd person singular form of pouvoir (to be able to / can).

Present tense of pouvoir:

• je peux
• tu peux
• il/elle/on peut
• nous pouvons
• vous pouvez
• ils/elles peuvent

Since cette photo is singular, French uses peut:

• Cette photo peut servir...

So the structure is:

• subject + peut
  • infinitive
• Cette photo peut servir... = This photo can serve...

Usually yes, but in many contexts it is also very close to evidence.

So:

• preuve = proof
• and often, depending on context, evidence

In this sentence, English might naturally say:

• This photo can serve as proof
• This photo can be used as evidence

Both are good ways to understand preuve here.