I don’t think this URL attribute is necessary if you intend to use a complex obs with Core’s ImageHandler. Out of the box the value_complex field/member will contain the necessary metadata telling the handler how to find the image.
However if you are not happy with the implementation of that handler, then you can always implement your own handler. However it will have to live somewhere… (meaning, ‘in some OMOD’).
Attachments is my baby so I’m rather keen on pushing it forward. But rather than implementing yet another handler (if you are unhappy with ImageHander) You could also use Attachments’ REST API to save and retrieve that image. I have always hoped to package Attachments with the Bahmni distro but this was never a priority high enough to get down to it.
See here for instance: Bahmni PAT call 20-Jun-2018 - QA/UAT for 0.91