All Start8 images should be three images stacked vertically above each other.
Once the _x1.png thing works correctly (as noted above we need to push an update as it is working backwards!) in order to make a suitable start button you would simply make all three the same image. So for example a start button of your wife would be resized to 32 pixels tall for each frame with each frame being identical and stacked together. Then you would use Start8 1.3 and name your image mywife_x1.png.
Start8 would then correctly add the darkened background areas on mouseover and pressed for you. This auto darken and pressed system is used by our new default image and by the Start8 logo option, though both of those are hardcoded.
As it happens we have a start button editor in development to make life easier for people so they can make more start buttons of their choosing as aligning images can get tricky and one of the options is to make Start8 add the mouseover and pressed states as while people can make one state, it is much harder to go and make other states as it requires more artistic talent.
As mentioned above the update later today will fix the _x1.png thing so that works correctly. Right now any image without _x1.png gets the mouseover and pressed button states replacing the current ones in the button image which is not what was intended.
While I cannot stop you using trademarked and copyrighted images, I would of course urge you to obtain permission from the rights holder if you were to go down that path.