Header picture resize

Well, that depends on the version of Excel that you are using. This may or may not be what you're looking for but in 2007...

Microsoft Office Excel 2007
1. Click the View tab.
2. Click in the header or footer section where the image is located.
3. Click in the &[Picture] text of the image.
4. On the Design tab under Header & Footer Tools, click Format Picture
in the Header & Footer Elements group.
5. On the Size tab, adjust the size of the image to fit inside the
header or footer section.
6. Click OK.