In zul, <image content="@load(vm.image)" /> will occur a casting error :

org.zkoss.zel.ELException: Cannot convert BufferedImage@125c99f: type = 1 DirectColorModel: rmask=ff0000 gmask=ff00 bmask=ff amask=0 IntegerInterleavedRaster: width = 200 height = 200 #Bands = 3 xOff = 0 yOff = 0 dataOffset[0] 0 of type class java.awt.image.BufferedImage to interface org.zkoss.image.Image
at org.zkoss.zel.impl.lang.ELSupport.coerceToTypeForSetValue(ELSupport.java:468)
at org.zkoss.zel.impl.parser.AstValue.setValue(AstValue.java:215)
at org.zkoss.zel.impl.ValueExpressionImpl.setValue(ValueExpressionImpl.java:256)
at org.zkoss.xel.zel.ELXelExpression.setValue(ELXelExpression.java:50)
at org.zkoss.bind.impl.BindEvaluatorXImpl.setValue(BindEvaluatorXImpl.java:50)
at org.zkoss.bind.impl.LoadPropertyBindingImpl.load(LoadPropertyBindingImpl.java:81)
at org.zkoss.bind.impl.PropertyBindingHandler.doLoadBinding(PropertyBindingHandler.java:171)
at org.zkoss.bind.impl.PropertyBindingHandler.doLoad(PropertyBindingHandler.java:372)
at org.zkoss.bind.impl.BinderImpl.loadComponentProperties(BinderImpl.java:1865)
at org.zkoss.bind.impl.BinderImpl.loadComponent(BinderImpl.java:1847)
at org.zkoss.bind.impl.BinderImpl.loadComponent(BinderImpl.java:1849)
at org.zkoss.bind.BindComposer.doAfterCompose(BindComposer.java:138)

but if use other way like <image content="${bi}" />, "bi" is declared in zscipt, it will work fine.