Return 1 pair by SQL Id SERVER

You could use APPLY (efficiently) to get the first of each row.

For example:

SELECT 
    A.IdentificadorAutomovil
   ,A.Titulo
   ,R.Imagenes
FROM Automovil A
    CROSS APPLY
( 
    SELECT TOP 1 I.Imagenes
    FROM Imagenes I
    WHERE I.Automovil = A.IdentificadorAutomovil
) R

DEMO

In case you want to group by car you would be using the GROUP BY operator as follows:

SELECT
    IdentificadorAutomovil ,
    Automovil.Titulo ,
    Automovil.Precio ,
    Automovil.Anio ,
    Automovil.Kilimetros ,
    Automovil.Ubicacion ,
    Imagenes.Imagenes
FROM
    Automovil
    INNER JOIN Imagenes ON Automovil.IdentificadorAutomovil = Imagenes.Automovil

GROUP BY 
    IdentificadorAutomovil,
    Automovil.Titulo ,
    Automovil.Precio ,
    Automovil.Anio ,
    Automovil.Kilimetros ,
    Automovil.Ubicacion ,
    Imagenes.Imagenes

The issue is that if the column of images differs from one another you will keep bringing 2 records, since it shows you one image per record.