Hi Feng. I know what you are asking, and why you would like to have this feature. Similar feature has already been requested, and I will definitely be looking into it at some point.
The only "challenge", is that I'm not sure this should really be a "rating" plugin. If we allow "like" or rating, it would be a public feature, available to all visitors. From there, "likes" or average rating would be stored per photo, and an image can have "14 likes" or "3.4 average rating (out of 5)". Also, to prevent same users from liking or rating an image multiple times, would require some login mechanism so likes are per user. I think in your case, you are looking for a way for a client to SELECT (check) images they like, and then send the list of "liked" images to you, perhaps in an email. I already have a "lightbox" feature planned, which is almost like a web-shop (where visitors can select images), and then "send order" ... This may be applicable in your case.
- I can filter these photos, either in the gallery or in the admin area, in order to find out which photos are selected.
The only challenge with that, is that the rating would be "public" and other people could rate the images. The only exception would be if you kept the specific gallery hidden or password-protected, so that only one user could rate it. Also, if it's rating or like
Anyway, I know what you are asking, and will definitely think about some solution for the future.