There are a lot of variables in play when comparing images. The Find method takes many more parameters than what you are providing. You might want to include something for the pixel tolerance, make sure the mouse isn't included, and possibly a color tolerance. Resolution differences can make a difference (between the saved image and the newly rendered image).
http://support.smartbear.com/viewarticle/55152/That page also has helpful links to
Why image comparisons fail and
Factors affecting image comparison
