Thank you, I did email them twice! No reply, though, but I attached a photograph with the required resolution too.
Also, I forgot to mention one thing- the 'Application inspector' was showing the application to be complete even before I uploaded the photograph. The inspector was showing the application incomplete until the mark sheets, passport, GMAT score etc. were uploaded, as these fields had an astirk (*) marked in front of them. But the photograph didn't. Nevertheless I uploaded a photograph before submitting the application, just like I mentioned.
Does it mean that it's not a mandatory field?
Secondly, no specific rule was mentioned outrightly regarding the resolution, and the upload tab just mentioned 'latest colour photo in 300 dpi', which I uploaded. It was only after I read the blogs and other posts that I inferred that they prefer passport size photos.
Also, unlike other documents, the photograph in particular was asked to be named as 'firstname_lastname.pdf'. Hence, it may be possible that the photograph is directly uploaded to a separate database