Classe les photos, même si les métadonnées changent.

Because Classe is the imperative form, used for giving a command or instruction.

• Tu classes les photos = You sort/classify the photos
• Classe les photos = Sort/Classify the photos

In French, commands often drop the subject pronoun (tu, vous, nous).

So this sentence is addressing one person directly.

This is a very common question. The verb is classer. In the present tense:

• tu classes
• il/elle classe

But in the affirmative imperative for -er verbs, French usually drops the final -s in the tu form:

• Tu classes → Classe !

So:

• Classe les photos = command to one person

A useful comparison:

• Tu regardes → Regarde !
• Tu fermes → Ferme !

One extra note: the -s can come back before y or en:

• Vas-y
• Manges-en

But in your sentence, there is no y or en, so it stays classe.

It is for one person.

• Classe les photos = command to one person (tu)
• Classez les photos = command to more than one person, or to one person formally (vous)

So if you were speaking to a group, you would say:

• Classez les photos, même si les métadonnées changent.

In French, nouns usually need an article much more often than in English.

So French says:

• les photos

where English might simply say:

• photos

Here, les is the plural definite article, and it is perfectly natural in instructions like this.

French often uses articles in places where English uses a bare noun:

• J’aime le café = I like coffee
• Ferme la porte = Close the door
• Classe les photos = Sort the photos

Même si means even if or sometimes even though, depending on context.

It introduces a contrast:

• Classe les photos, même si les métadonnées changent.
• Sort/classify the photos, even if the metadata changes.

So the idea is: Do it anyway, despite that possible change.

It is a very common expression in French.

Because si by itself usually just means if.

• si = if
• même si = even if

Adding même strengthens the contrast.

Compare:

• Si les métadonnées changent, classe les photos.
  = If the metadata changes, sort the photos.

• Classe les photos, même si les métadonnées changent.
  = Sort the photos, even if the metadata changes.

The second sentence suggests that the action should happen regardless of that condition.

In French, métadonnées is normally treated as a plural noun, like metadata understood as multiple pieces of data.

So French usually says:

• les métadonnées

not:

• la métadonnée unless you mean one single metadata item

Because the subject is plural, the verb must also be plural:

• les métadonnées changent

Also, métadonnées is feminine plural:

• la métadonnée
• les métadonnées

Because the subject is plural:

• les métadonnées = the metadata

So the verb must agree with that plural subject.

The verb is changer in the present tense:

• je change
• tu changes
• il/elle change
• ils/elles changent

Since les métadonnées is plural, French uses:

• changent

One pronunciation tip: the -ent ending in this form is usually not pronounced. So change and changent sound the same in normal speech.

It is present indicative.

After même si, French normally uses the indicative, not the subjunctive.

So:

• même si les métadonnées changent

is standard and expected.

That is different from some other expressions that trigger the subjunctive. Here, French treats the clause as a real or possible situation, so the indicative is used.

They are similar, but not always identical.

In this sentence, classer suggests:

• classifying
• organizing
• putting into categories or order

Trier often means:

• sorting
• separating items according to a criterion

Depending on context, both might work, but the nuance can differ:

• Classer les photos = organize/classify the photos
• Trier les photos = sort through the photos

If the idea is putting photos into albums, folders, or categories, classer is very natural.

A simple approximate pronunciation is:

Class les fo-to, mem si lay may-ta-do-nay shanj

A few helpful points:

• Classe sounds like class
• les sounds roughly like lay
• photos = fo-to
• même si = mem si
• métadonnées = may-ta-do-nay
• changent sounds roughly like shanj

And remember: the final -ent in changent is silent.