Try attaching to chart's BeforeLayout
event and then set the picture you'd like to use as a custom figure like this:
radChart.BeforeLayout += new EventHandler<
void radChart_BeforeLayout(object sender, EventArgs e)
radChart.Legend.Items.Marker.Appearance.Figure = "Rectangle";
radChart.Legend.Items.Marker.Appearance.FillStyle.FillType = Telerik.Charting.Styles.FillType.Image;
radChart.Legend.Items.Marker.Appearance.FillStyle.FillSettings.BackgroundImage = "C:\\Pictures\\ChartImage.png";
Using this approach should set a custom image as a legend item marker.
Hope this helps.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed