I forgot to answer your question about copying.  If you do something like `im2 = im` and `im` has the extra info, then `im2` will too.  However, if you use the `copy` function: `im2 = im.copy()` then it won't have the extra info as it is currently written.  If it is desired to preserve it, we could update the copy function, but I suspect an `added_flux` values is probably only relevant directly have a `draw` call, so I wouldn't worry about keeping it in copies.

Anyway, I went ahead and made this change.  I think I'm persuaded that this is a good way to go.  It's easy to revert if people prefer having `added_flux` returned as part of a tuple.