Inverse Projection

[Giridhar Manepalli]

Hello All,
When the user clicks on the map image, I calculated the
Latitude/Longitude using javascript. This pretty much assumes linear
transformation of image points to lat/long which obviously will be
erroneous. The deviation from the actual lat/long will depend on the
"projection" i have used for my shapefile.

Currently, I dont have any information of the projection system used.

Is it possible to identify more accurately the lat/long of the mouse
click without knowing the projection system?

If I know the projection system used, is it right to say that I can
accurately calculate the lat/long of the mouse click? If so, how?

I appreciate if anyone can throw some light on these issues!

Thanks
Giridhar