Starting now you can make your Multi-Plant images private. There are numerous options for this:
1) When you add a multi-plant image, you will see the option to make it private.
2) For existing images, you'll see the privacy options when you view the image itself.
Why would you use this feature? Primarily for mapping gardens. For example, Jon has some daylily beds and he wants to take birds-eye view photos of them, upload them, and tag each clump as to which daylily is which. None of them are blooming, though, and so it's not a nice "garden" picture. But the tagging functionality is perfect for making a map. The privacy settings ensure it doesn't show up with all the beautiful landscape shots.
If you have private multi-plant images, nobody will see them but you and they are not included in your image totals. You can experiment and use a private browsing window (consult your browser's documentation) to confirm for yourself that the privacy settings are working.