Thank you for writing.
By default we have an image converter that converts the image to base64 string. These strings are used by our theming functionality where the string can be converted to image.
What you can do in this case is to create a custom menu item and use another image converter:
MyItem : RadMenuItem
.Image = value;
The above example uses the default .NET image converter but you can use your own as well.
Please let me know if there is something else I can help you with.
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