It might be useful to note that iNat did do a major push asking users to consider changing licenses if they were comfortable with it about three years ago when iNat became part of Amazon’s ODP. See blog post here:
https://www.inaturalist.org/blog/48165-we-want-you-to-license-your-inaturalist-photos-before-april-15th
with link to forum post: https://forum.inaturalist.org/t/we-want-you-to-license-your-inaturalist-photos-before-april-15th/21430
Staff noted that, as of 3/24/2021
“Currently about 66% of iNaturalist photos are licensed. We’d love to get this up to 75% or 85% with your help before April 15th to help us cut costs and spread the benefits of iNaturalist more widely!”
This is a significantly higher proportion of licensed images than reported by @Loopy30 above. I would guess it suggests that lower volume observers are more likely to choose All Rights Reserved while higher volume observers are more likely to have some type of CC license. This makes some inherent sense to me, as higher volume observers are probably generally more engaged and aware of license choices.
In April 2021, staff noted that the campaign did have an impact:
It would be interesting to know the current license breakdown for iNat media. If those gains are sustained, it could also suggest whether reaching out to newer users (ie, those who have joined in the 3ish years since that campaign) might have a strong positive effect. It seems like the last campaign had an effect of about +4%, which sounds small, but it means that almost 12% of All Rights Reserved media at the time were changed to a CC license as a result of that campaign. I think that’s pretty good. If those users also updated their current licensing options (as opposed to just changing the license of previous observations), and this seems most likely, the gains could be sustained. Given the rapid growth of iNat, encouraging new users to choose open licenses could have proportionately larger impacts (in terms of number of photos/observations) than focusing on asking existing users to change the license of previously made observations.
On a side note, I do think a really good opportunity for asking existing users to consider their licenses is coming up when the new app is released. When users sign in to the new app for the first time, they could see a prompt showing their current licenses and asking to confirm them, or the giving options to change (with a short message touting the benefits of open licenses).