Hi Ben,
Thank you for posting query to us.
You can use ComboBoxAdv.ImageList property to get/set ImageList for control and ComboBoxAdv.ImageIndexes property to set image Index for specified item.
//assign first image in ComboBoxAdv.ImageList to second item in items list.
this.comboBoxAdv1.ImageIndexes[2] = 0;
Then use ComboBoxAdv.ShowImageInTextBox property to show images in TextArea and use ShowImagesInComboListBox in the Listbox.
Please refer the sample which implements the above said feature:
http://websamples.syncfusion.com/samples/Tools.Windows/F67325/main.htmPlease refer this KB article which explains "How do I assign images to ComboBoxAdv items?"
http://www.syncfusion.com/support/kb/tools/Default.aspx?ToDo=view&questId=406Kindly let us know if you need any further assistance.
Thank you for using Syncfusion Products.
Best Regards,
Jeba.