Hi Willis,
Thank you very much for interest on Syncfusion products.
I am afraid that i could not able to reproduce the issue at my side. I have created a simple sample which receives the image in byte array from a web service and add that picture to the worksheet and it is tested with the 8.2.0.18(Syncfusion Silverlight assemblies).please try the sample from the below link and let me know if this helps you.
Sample link:
http://help.syncfusion.com/samples/XlsIO.Web/94958.zipPlease, let me know if you need any clarifications.
Thanks,
Lokesh