It is obvious that we close popup when we click on dark area, on close button, or press escape key. But should we close it when we click on center image?
Let's assume that there are three scenarios, what should happen after clicking on center image:
Thank you!
Personally I think that closing a single image by clicking on it it's a good idea since it will minimize mouse movements (and improve ux on small touch screens where it's hard sometimes to tap the close button).
Concerning multiple images I think that clicking an image should open next image because of the same reason (and close or restart the gallery at the end).
It's always a good idea to let users do something with minimum movement.
BTW, I think that it's better to place close button at the corner of the image because placing it at the corner of the screen will require more movement (not experienced users will try to click the cross instead of clicking somewhere else to close an image).
Clicking an image can do one of two things:
(1) Nothing, which would be the desired behavior... or
(2) Enlarging the image, preferably in the modal dialog you're showing. But this assumes that larger versions of the images is available. If not, then nothing should happen.
I think that both type of functionality are common. Facebook demonstrates a nice example where clicking on the image shows the next one.
However, if there is no salient distinction between the first mode of a single picture and the second mode of multiple pictures, I'd go with a click showing the next picture. This is just useful for most of the time, but for cases of a single picture, don't make the user think in what mode she is in.
