Hi ha una foto penjada a la paret, sobre la catifa.

Hi ha is the standard Catalan way to say there is or there are.

• ha comes from the verb haver
• hi is a little locative element that is part of this fixed expression

So:

• Hi ha una foto = There is a photo
• Hi ha fotos = There are photos

You should usually learn hi ha as a single chunk.

Because foto is feminine in Catalan.

Even though it ends in -o, it is short for fotografia, which is clearly feminine. So it takes:

• una foto
• la foto

This is something English speakers often notice because the ending may look misleading at first.

Penjada describes the photo. It means hanging or hung, depending on how you translate it naturally into English.

It agrees with foto, so it is feminine singular:

• masculine singular: penjat
• feminine singular: penjada
• masculine plural: penjats
• feminine plural: penjades

So:

• una foto penjada = a hanging photo / a photo hung up / a photo that is hanging

In this sentence, it works like a postposed adjective or a reduced relative clause: a photo hanging on the wall.

In Catalan, adjectives and participle-based adjectives normally agree with the noun they describe in gender and number.

Here, foto is:

• feminine
• singular

So the form must be penjada.

If the noun changed, the adjective would change too:

• un quadre penjat
• unes fotos penjades

This kind of agreement is much more visible in Catalan than in English.

Catalan often uses a for location where English uses on, in, or at, depending on the context.

So penjada a la paret is the normal way to say hanging on the wall.

Word for word, English speakers may expect something like on the wall, but Catalan uses a very naturally here.

So just learn:

• a la paret = on the wall

Sobre usually means over, above, or on top of, depending on context.

In this sentence, sobre la catifa tells you the photo’s position relative to the carpet: it is above the carpet.

So the idea is:

• there is a photo
• it is hanging on the wall
• it is above the carpet

Catalan sobre does not always mean physical contact. Very often it simply means over/above.

The structure is:

• Hi ha
  • thing that exists + descriptive information about it

So here we get:

• Hi ha = there is
• una foto = a photo
• penjada a la paret = hanging on the wall
• sobre la catifa = above the carpet

Catalan often puts descriptive material after the noun, so una foto penjada is completely normal.

Yes. A fuller version could be something like:

• Hi ha una foto que està penjada a la paret...

That is grammatically possible, but the original sentence is more compact and natural.

Catalan often prefers the shorter descriptive form when the meaning is clear:

• una foto penjada a la paret

instead of

• una foto que està penjada a la paret

English does something similar with a photo hanging on the wall.

It works for both singular and plural in modern Catalan.

So you say:

• Hi ha una foto = there is a photo
• Hi ha dues fotos = there are two photos

Unlike English, the form does not change between singular and plural.

Yes. Foto is the common shortened form of fotografia.

So these are both correct:

• Hi ha una foto penjada a la paret...
• Hi ha una fotografia penjada a la paret...

Foto is extremely common in everyday speech and writing, while fotografia is a bit more formal or full.

Because Catalan does not need to build this idea in exactly the same way as English.

English often says:

• There is a photo hanging on the wall

Catalan can do the same kind of compact description with:

• Hi ha una foto penjada a la paret

So penjada directly describes foto without needing an extra is in that part of the sentence.

A more expanded version with a verb is possible, but not necessary.