Currently, the Editor's ImageBrowser dataSource only uses the default name, size, and type fields: https://docs.telerik.com/kendo-ui/api/javascript/ui/editor/configuration/imagebrowser.schema.model.fields#imagebrowserschemamodelfields

Additional custom fields coming with the response (sent back to the client by the specified end point) are ignored and are not accessible in the ImageBrowser's dataSource.