Bug 104986 Backgound image uses an absolute path
Currently Chart uses an absolute path to indicate a backgournd image, that may cause the design unusable on other environments. Expected the background image can be definded in multiple ways like in report designer. e.g. URI(absolute path), File(relative path), Embedded Image(Encoded Image Data).
chart/org.eclipse.birt.chart.device.extension/src/org/eclipse/birt/chart/device/swing/SwingRendererImpl.java
are.getBackground( ),
				_ids );
		if ( cFG == null ) 
		{
			return;
		}
		
		final GeneralPath gp = new GeneralPath( );
		PrimitiveRenderEvent pre;
		for ( int i = 0; i < are.getElementCount( ); i++ )
		{
			pre = are.getElement( i );
			if ( pre instanceof ArcRenderEvent )
			{
				final ArcRenderEvent acre = (ArcRenderEvent) pre;
				final Arc2D.Double a2d = new Arc2D.Double( acre.getTopLeft( )
						.getX( ),
						acre.getTopLeft( ).getY( ),
						acre.getWidth( ),
						acre.getHeight( ),
						acre.getStartAngle( ),
						acre.getAngleExtent( ),
						toSwingArcType( acre.getStyle( ) ) );
				gp.append( a2d, true );
			}
			else if ( pre instanceof LineRenderEvent )
			{
				final LineRenderEvent lre = (LineRenderEvent) pre;
				final Line2D.Double l2d = new Line2D.Double( lre.getStart( )
						.getX( ),