Thanks for all the suggestions. Just paying Google to increase storage may be an option, I'm not sure because I use the no longer available free Google Apps, now "Google Suite Legacy". I suspect I can't add paid for storage without moving to one of the current plans. One option might be to use a separate Google account, either within my domain or a separate stand-alone Gmail account, and use that just for photos. 15Gig would be plenty if not shared with Google Drive and email.
Something I need to follow up is that Idrive, that I use for online backup, offers a specific photo version, however it seems to be limited to use from Android and IOS mobile devices. I need to investigate whether that can be bolted onto my existing backup account, which has plenty of space available.