There’s two ways.
COMMENTS (yes, they’re back!). This time, click on someone’s Topic with the image and simply add a Post with the comment (or question).
LIKES just click on the LIKE button if you don’t really want to say anything but you want to show your appreciation of the image. Your ‘Like’ will appear on their Post and they’ll know it’s from you.
PLEASE REMEMBER … you may put Comments onto another member’s Personal Image topic but YOU MUST NOT post any photographs in their space.