图片水印，小图片正常，大尺寸不正常

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好像大尺寸就没有水印，F12如下，
img class="alignnone size-full wp-image-1237" src="http://file.wangzhuan58.cn/wp-content/uploads/2017/06/2017062516461563.png?watermark/1/image/aHR0cDovL2ZpbGUud2FuZ3podWFuNTguY24vd3AtY29udGVudC91cGxvYWRzLzIwMTcvMDYvMjAxNzA2MjUxNDA3MjQ5Ny5wbmc=/dissolve/100/gravity/SouthEast/dx/20/dy/20|imageslim|imageView2/2/w/1016/h/480/q/90" alt="" width="1016" height="480" srcset="http://file.wangzhuan58.cn/wp-content/uploads/2017/06/2017062516461563.png 1016w, http://file.wangzhuan58.cn/wp-content/uploads/2017/06/2017062516461563-768x363.png 768w" sizes="(max-width: 1016px) 100vw, 1016px"
小尺寸有水印，F12如下
img class="alignnone size-medium wp-image-1238" src="http://file.wangzhuan58.cn/wp-content/uploads/2017/06/2017062516462379.png?watermark/1/image/aHR0cDovL2ZpbGUud2FuZ3podWFuNTguY24vd3AtY29udGVudC91cGxvYWRzLzIwMTcvMDYvMjAxNzA2MjUxNDA3MjQ5Ny5wbmc=/dissolve/100/gravity/SouthEast/dx/20/dy/20|imageslim|imageView2/2/w/763/h/378/q/90" alt="" width="763" height="378"