How to validate an image before saving in a file

I have a function that saves the image in the respective folder.

I want to check if the image already exist in the folder , first with name if the name are same then with the SHA1 of the image

My current function looks something like this

function descargarImagen($id,$url,$pais1)
{


    $ruta = rutaBaseImagen($id,$_POST['pais']);

    $contenido = file_get_contents($url);

    $ext = explode('.', $url);
    $extension = $ext[count($ext) -1];

    $imagen['md5'] = md5($contenido);
    $imagen['sha1'] = sha1($contenido);
    $imagen['nombre'] = $imagen['md5'].'.'.$extension;

    $ficherof = $pais[$pais1]['ruta_imagenes'].'/'.$ruta.'/'.$imagen['nombre'];
    $ficherof = str_replace('//', '/', $ficherof);

//Here before putting the file I want to check if the image already exist in the folder


    file_put_contents($ficherof, $contenido);

    $s = getimagesize($ficherof);

    $imagen['mime'] = $s["mime"];
    $imagen['size'] = $s[0].'x'.$s[1];
    $imagen['url'] = $urlbase_imagenes.'/'.$ruta.'/'.$imagen['nombre'];
    $imagen['url'] = str_replace('//', '/', $imagen['url']);
    $imagen['date'] = time();
    $imagen['fichero'] = $ficherof;

    return $imagen;
}

I am trying to validate in two ways 1.If the name of the image is present in the folder or not . 2.If present then check if the image is same or different , because there could be new image but same name

Any suggestion will be appreciated

Thanks in Advance