Ms-Office from 2010 version gives you a wonderful tool called screen clipping, which is available in Word, Powerpoint and Excel whereby you can select any tiny portion of the picture you like and paste it to the file or even save it as a different image altogether.
It not only reduces the file size, but also save time of cropping re-designing, etc if you do the Printscreen option.
The great advantage of this tool is, it doesn't compromise the quality and resolution of the image. You can even take different clippings of the same file and combine them to make a single file.
The screenshot option is available in the Insert tab.