how to determine size of jpeg primary image

[suchiramehta]

hi
i have to design a program which recovers image files from digital media after we format it.
i am able to recover all exif data but i am not getting size of primary image in bytes.
i am trying to read total number of bytes from SOI marker with corresponding EOI marker.
if anyone knows please help.
please tell weather i am proceeding in the right direction.

thanks n regards