This is an interesting study, and definitely, agree that there's room for testing lots of other factors around the results! Her conclusion that "While these experiments provide some insight into the world of adoption photos, the information they give shows us that the specifics of shelter dog photography may not be as important as many people seem to suggest" definitely hits on one of my favorite mantras of "not letting perfect be the enemy of good". There are countless small things we can do to improve shelter photos that will inevitably lead to more exposure and more attention for our animals and organizations. I think it's hard to draw broad-based conclusions about some of the factors, given that appeal and attention are so subjective.
However, another recent research project is this one, that helps identify some of what adopters identified as most important in terms of how the dogs appear and what they are shown, as well as how often they used things like online photos to make decisions about adoption prospects. https://www.heartsspeak.org/how-photos-are-important-to-pet-adoption-a-study/ Infographic for this study is attached and has some really interesting info!
In terms of achieving some of what the author touches on and beyond, there are lots of ways to achieve a fairly uncluttered and almost solid-looking backdrop in a shelter environment by using a shallow depth of field (or portrait mode, on a cell phone!), even outdoors or in kennels/cages. We have some resources and examples that help show and describe this here: https://www.heartsspeak.org/project/shelter-photography-basics-part-3-getting-great-photos-anywhere/ and https://www.heartsspeak.org/project/guide-to-taking-great-cell-phone-photos/
I hope this is helpful in taking some of the data and creating real-world applications :)