修改web.config配置,设置大小,或者关闭限制(totalBehavior="ignorelimits"
<configuration> 

<configSections> 
    <section name="resizer" type="ImageResizer.ResizerSection" 
requirePermission="false" /> 
</configSections> 
<appSettings> 
.... 
</appSettings> 
<resizer> 
    <sizelimits imageWidth="0" imageHeight="0" totalWidth="5200" totalHeight="5200" totalBehavior="throwexception" /> 
</resizer>