That is already possible as long as the machine you are hosting photoprism on is already open to the internet. You can create a shareable link to an album (dont know about individual pictures) which gives people read-only access to that specific album and nothing else

This is the main reason why I still use Google Photos. I have shared albums with my family, that automatically add photos using facial recognition. If I want to create an album for an event and share with people it's really easy.