HI
This is off the cuff - but may help your approach to this. (I too have a medical client)
We know Google can't see the image (yet!!)
It can read the jpg file name and alt tag
Two ideas:
If it is a new service why not password protect the area with sensitive photos
or
Create a link which takes them to a gallery. Explain the link is to a gallery with photos that may be distressing.
that they click agree to continue and could always have a data capture to prevent children finding it
You could then have the gallery pages with a no follow robot so the page is not cached and they aren't found through any search, and that way you can still optimise the rest of the site / or hold onto your existing rankings
Further to this if there were any 'before' and 'after' photos that could be displayed - they could be done in page and the link for more case studies underneath.
Also
If you were concerned about any language you may have to use embed it in a graphic button.
Just a few thoughts.
Let me know what you do, I will be interested
PH