Required library edition:
Required library file: dhtmlxgrid_drag.js

redefine this method in your code to define how grid row values should be displaied while draging

• id - id of grid row

Returns html string representing dragging row

 grid.rowToDragElement=function(id){
            //any custom logic here
            var text = "<img src='some.gif'> - "+grid.cells(id,0).getValue(); // prepare a text string
            return text;
        }

See also: treeToGridElement