Update SQL table with random value from other table

Question

On Microsoft SQL Server 2008, I have a table with Products:

Id | Name | DefaultImageId

And one with Images:

Id | ProductId |

Answer 1

Addressing @philreed's issue with the selected answer:

Is there a way to assign each row being updated with a different value randomly chosen from the source table?

UPDATE Products
SET DefaultImageId = t2.Id
FROM Products t1
CROSS APPLY (
    SELECT TOP 1 Id
    FROM Images
    WHERE t1.Id = t1.Id
    ORDER BY newid()
    ) t2