Which version of Crystal are you using? In XI (I believe) and above (I know this is in 2008 and 2011) you would do the following:
1. Right-click on the image object and select "Format Graphic"
2. Go to the Picture tab.
3. Click on the button by "Graphic Location"
4. Select the field that contains the location of the image.
5. Make sure that Scaling is set to 100%.
6. Go to the General tab and turn on "Can Grow"
7. Click on OK.
-Dell