Is there a digital camera that is able to save people bounding boxes?

Advancements in the photographic field is drastic but such an idea has not struck yet :) but there is definitely an alternative to recognize faces and add tags to the pictures.

Picasa photo editor has this function.

http://support.google.com/picasa/answer/156272?hl=en

Nikon RAW holds the face detection data but does not do any actual recognition since it's too computationally expensive to do in camera.

Windows Live Photo Gallery will do the face recognition and will output to XMP according to http://blogs.msdn.com/b/pix/archive/2008/10/02/why-people-tags.aspx

My Canon S110 can recognize faces and identify them! There's a menu in the camera for saving up to 10 faces.

As far as I know, they are put as tags in Lightroom when I import the photos in my computer.

My comparatively old Panasonic DMC-FZ200 (released 2012) has this in the manual for play mode:

[Face Rec Edit]
You can delete or change the information relating to Face Recognition for the selected picture.
1 Select [Face Rec Edit] on the [Playback] menu. (P52)
2 Press 3/4 to select [REPLACE] or [DELETE] and then press [MENU/
SET].
3 Press 2/1 to select the picture and then press [MENU/SET].
4 Press 2/1 to select the person and then press
[MENU/SET].
5 (When [REPLACE] is selected) Press 3/4/2/1 to

[...]

Note
• When all Face Recognition information in a picture has been canceled, the picture will not be
categorized using Face Recognition in [Category Selection] in [Filtering Play].

So it does recognise several faces (I think you can store about 10 faces it should recognize by name) and will prioritise them when doing face-based focusing. It will also label them on playback and allow selective playback of images containing them.

I haven't used this functionality so I don't know which form it is stored in: I would suspect some EXIF tags getting used rather than XMP (but of course this should be reasonably straightforward to convert). Since this sounds like the kind of feature earning a checkmark in camera tests and since it already was available in 2012, I should be surprised if it isn't buried somewhere in the menus of most current-day offerings in some more or less useful manner.