In the meantime [ccdproc](https://github.com/astropy/ccdproc/) has emerged which has a `CCDData` class as an `NDData` sub-class ... I'm not sure if `photutils` should be aware of `CCDData` contents or if it should be more of a toolbox that e.g. sums arrays over apertures that is called by `ccdproc` and other packages.

I think I'd prefer the "toolbox" approach so that `photutils` becomes usable e.g. also for count data in [gammapy](https://gammapy.readthedocs.org/en/latest/), but for very common cases like CCD data it could also be OK if `photutils` is `CCDData`-aware?

@mwcraig @crawfordsm What do you think how `ccdproc` and `photutils` should work?