Hi ganesh,
I would say, an image should make you ask questions. It ideally should make you think. What's going on? Why are things the way shown in an image?
This does make you ask, make you think. The image should work hard (like they have said in the Oil Spillage series of 6 images - the series should work without words) to trigger thoughts in your mind. And maybe a few words as a caption answer those questions. Captions, i believe are important to set some context to an image.
On a more personal level, i still have far to go to achieve the "unsupported yet vocal" image!!
Maybe my image doesn't belong on this forum...? i am still exploring what does and what may not
A