Hi @margot welcome to the /e/ forum.
It might seem slightly odd but when you send photos by text they are actually sent by your carrier’s MMS service.
One needs the carrier to have provided you with an MMS service for this.
In the case where one knows that the carrier does provide one with MMS service sometimes /e/ users seem to find that the carrier has not always set that up automatically as one would expect.
I just ring the carrier and ask for the APNs to be sent to the device …
An alternative method was also given recently here New user: no mobile internet service