I see you have learned nothing in a year and 9 months!
https://www.mobileread.com/forums/sho...d.php?t=166836
The last I recall this "image and caption" being brought up was in this topic, with RbnJrg's (non-SVG) code:
https://www.mobileread.com/forums/sho...d.php?t=223178
Doing something with HTML+CSS would probably have slightly better support/compatability/convertability (I don't know how well something like Calibre would handle converting a slightly more complex SVG?). Although I would be interested in an SVG solution as well. I know I am slacking in my SVG learning.