Each variation has its own set of images and those images are returned by the VariationImages response group, for example:

  <SmallImage>
    <URL>  http://images.amazon.com/images/P/B99999999A.01._SCTHUMBZZZ_.jpg
    </URL>
    <Height Units="pixels">60</Height>
    <Width Units="pixels">60</Width>
  </SmallImage>

  <MediumImage>
    <URL> http://images.amazon.com/images/P/B99999999A.01._SCMZZZZZZZ_.jpg
    </URL>
    <Height Units="pixels">140</Height>
    <Width Units="pixels">140</Width>
  </MediumImage>

These images are small and medium size images of the same child variation. For more information about image sets and variation images, see Motivating Customers to Buy.