GridImageColumn is available from Q2 2009 BETA (version 2009.2.616)
release onwards. You may use a GridTemplateColumn to achieve the desired scenario. Add the image in the ItemTemplate of the GridTemplateColumn. Refer the following help article which explains how to dynamically add a Template column to RadGrid.
Go through the section entitled 'Creating template columns programmatically' in the article. Programmatic creation