var imageList = new Ext.data.Store({
        autoLoad:true,
        reader:new Ext.data.JsonReader({
            totalProperty:'results',
            root:'items',
            fields:[
                 'picName','picUrl'
                ]
        }),
        proxy:new Ext.data.HttpProxy({
            url:"findImg_findPic.action"
        })
    })
        var tpl = new Ext.XTemplate(

    '<tpl for=".">',

        '<div class="thumb-wrap" id="{picName}">',

        '<div class="thumb"><img src="{picUrl}" title="{picName}"></div>',       

    '</tpl>',

    '<div class="x-clear"></div>'

    );

panel=========================
items:[new Ext.DataView({

        store: imageList,

       tpl: tpl,
       autoHeight:true,
       multiSelect: true,
      
       overClass:'x-view-over',

       itemSelector:'div.thumb-wrap',

        emptyText: 'No images to display'

   String path = request.getContextPath();
   String basePath = request.getScheme() + "://"
      + request.getServerName() + ":" + request.getServerPort()
      + path + "/";

------解决方案--------------------
显示图片我一般是直接再写个action来处理，直接用img标签显示会有这个问题的
action写法
public String showImage() throws Exception { 
       // 根据图片地址构造file对象 
       File file = new File(imageUrl); 
       InputStream is = new FileInputStream(file); 
       Image image = ImageIO.read(is);// 读图片 
       String imageType = imageUrl.substring(imageUrl.lastIndexOf(".") + 1); 
       RenderedImage img = (RenderedImage) image; 
       OutputStream out = response.getOutputStream(); 
       ImageIO.write(img, imageType, out); 
       out.flush(); 
       out.close(); 
       return null; 
   } 

jsp页面
src='showImage.action?imageUrl="+imgUrl+"'/>