var pic = "";

var smallPic  ='<img src="pics/Bobcat/bobcat0086S400x300.jpg" width="200" height="150" alt="Bobcat Moves Tree" />';
var middlePic ='<img src="pics/Bobcat/bobcat0086S400x300.jpg" width="300" height="225" alt="Bobcat Moves Tree" />';
var largePic  ='<img src="pics/Bobcat/bobcat0086S400x300.jpg" width="350" height="262" alt="Bobcat Moves Tree" />';
var bigPic    ='<img src="pics/Bobcat/bobcat0086S400x300.jpg" width="400" height="300" alt="Bobcat Moves Tree" />';

var sw = screen.width;

if (sw > 1280)
  pic = bigPic
else if (sw > 1054)
  pic = largePic
else if (sw > 800)
  pic = middlePic
else
  pic = smallPic;
  

document.write(pic);