Get image thumbnail via SOAP call

I am trying to display products in my store through a third-party application using the Magentos web services API. When I request image data for an item using "catalog_product_attribute_media.list", I get something like this:

Array
(
    [0] => Array
        (
            [file] => /a/k/akio-dresser.jpg
            [label] => 
            [position] => 1
            [exclude] => 1
            [url] => http://example.com/magento/media/catalog/product/a/k/akio-dresser.jpg
            [types] => Array
                (
                    [0] => thumbnail
                    [1] => small_image
                    [2] => image
                )

        )

)

This tells me that I should be able to get a version of this "sketch" or "small_image", but I cannot figure out how to actually do this. I looked through the documentation and tried everything I could, but was not successful. Does anyone else know which SOAP call I can use? Calling catalog_product_attribute_media.info seems to return exactly the same information, and catalog_product_attribute_media.types does not seem to return anything.