how can estimate the sampling frequency of image

hello how can estimate the sampling frequency of arbitrary image in matlab ,from image itself only,or how can estimate maximum frequency of image in matlab to calculte the actual sampling frequency does the aliasing effect the maximum frequency.

[Anan Yaghmour]

You can find this information simply outside Matlab. Right click on the image >> choose Properties>>Deails>>then look for the DPI(DOT PER INCH) number