Applet为什么不能看到gif图形

//源程序清单
import java.awt.*;
import java.applet.*;
public class ShowImage extends Applet
{
Image picture;
public void init()
{
picture=getImage(getCodeBase(),"Img.gif");
}
public void paint(Graphics g)
{
g.drawImage(picture,0,0,this);
}
}<HTML>
<TITLE>Show Image Applet</TITLE>
<APPLET CODE="ShowImage.class" WIDTH=600 HEIGHT=400>
</APPLET>
</HTML>在jdk1.5.02下用命令javac 编译为什么不能看到gif图形