On our practices, the image service editor (in desktop ArcGIS 9.3/9.3.1 & 10) does not provide any 'very effective' configuration or automatic functions to help us re-define footprints on user's needs, for example, to remove 255 255 255 or any artifacts along imagery boundary, which may affect interpretation after merging.
So, after finishing the wizard, the first thing to do is: manually to edit individual footprint one by one until satisfied, and save your modified footprints. And then, at least, the following steps should be used:
�?� re-build image service boundary; �?� remove the previous overviews; �?� re-define overviews; �?� ... and finally, �?� re-generate derived images & re-compile image service
If having ArcGIS 10 installed, you can have many automatic functions to do so in Mosaic Dataset. However, it is worth to mention that, very often you are still required to conduct manually-editing operation on some of footprints or boundary, even though the automation can remove majority of artifacts in ArcGIS 10.