calculate image resolution Php Resolution Detection?

[iGuest 3]

calculate image resolutionPhp Resolution Detection?

Hi ,I am use this script, but I have one problem when I am upload the image can I calculate the resolution of that image because I have a condition if resolution is less than 72 dpi image is reject to crop else if it is greater than 72 dpi image will go to crop.Here is a problem to how to calculate directly resolution of image. I am use formula for resolution is pixels/inches. But is failed to some cases.Please suggest me to how to get resolution of image if you have input as image size only .

-Santy