motool statement

Question

i have following statement

     var my_img = new Element ('img' , {'src' :'progress-green.gif' , 'style' : 'width:50px; border:3px solid red' }).inject(file.element, 'top') ;

when i modify the above statement like

              var my_img = new Element ('img' , {'src' :'+json.get('fpath')+' , 'style' : 'width:50px; border:3px solid red' }).inject(file.element, 'top') ;

its giving error ?

actually i am passing path of image...

Thanks