Bijo, you won't get much at all depending on the image, because the jpeg format *is* already compressed. Trying to recompress an already compressed data stream usually doesn't elicit very good results. As alternatives you can try Winrar and Winace. Winrar is good and the .rar format can usually give the 7z format a run for it's money, usually they're almost dead even, the problem is Winrar is shareware/payware. Winace is old and also payware, I haven't used it in ages, it's another multimedia compression format that isn't very common anymore. If Winrar and 7z can't give you the results you want, you're going to have to break up the images into small archives to send via email (many ISPs limit message size, some as small as 1 MB) or find another way to get it to him.

Good luck mate.