Hi Shannon,
1) Currently XlsIO 4.1 has no API support for inserting images in header and footer. We have already logged feature request with the development team. [#161].
2) XlsIO has the capability of loading preexisting image in the header and footer form the template file. Here is the sample that opens and resave the template file containing image in header and footer of excel file.
Sample
Please let me know if you have any questions.Thanks for using Syncfusion Products.
Thanks,
Ramu.K