Please try with the below code snippet.
ASPX
<telerik:RadComboBox runat="server" ID="RadComboBox1">
<Items>
<telerik:RadComboBoxItem Text="Select Job Type" Value="Select Job Type" />
<telerik:RadComboBoxItem Text="Long Term" Value="Long Term" />
<telerik:RadComboBoxItem Text="Short Term" Value="Short Term" />
<telerik:RadComboBoxItem Text="Last Minute" Value="Last Minute" />
</Items>
<ItemTemplate>
<div>
<asp:Image ID="Image1" runat="server">
<asp:Label ID="Label1" Text='<%# Eval("Text") %>' runat="server">
</div>
</ItemTemplate>
</telerik:RadComboBox>
ASPX.VB
For Each item As RadComboBoxItem In RadComboBox1.Items
Dim Image1 As Image = DirectCast(item.FindControl("Image1"), CheckBox)
Image1.ImageUrl = "Please add image url here"
Next