Hi Dennis,
Thank you for your interest in Syncfusion Products.
Currently Essential XlsIO do not have the support for exporting chart as an image. Entire worksheet can be converted to an image. Please refer the following link for more details.
http://help.syncfusion.com/ug_83/Reporting/XlsIO/ASP.NET/default.htm?turl=Documents%2Fconverttoimage.htmPlease let us know if you have any questions.
Regards,
Poornima