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.engine/src/org/eclipse/birt/chart/render/AxesRenderer.java
startX = ( i > 0 ) ? ( i - 1 ) : 0;
				break;
			}
		}
		for ( int i = 0; i < xa.length; i++ )
		{
			if ( xa[i] >= center + width / 2d )
			{
				endX = i;
				break;
			}
		}
		double yc = above ? Double.MAX_VALUE : 0;
		for ( int i = startX; i <= endX; i++ )
		{
			yc = above ? Math.min( yc, ya[i] ) : Math.max( yc, ya[i] );
		}
		return above ? ( yc - height - gap ) : ( yc + gap );
	}
	/**
	 * Renders all marker ranges associated with all axes (base and orthogonal)
	 * in the plot Marker ranges are drawn immediately (not rendered as
	 * deferred) at an appropriate Z-order immediately after the plot background
	 * is drawn.
	 * 
	 * @param oaxa
	 *            An array containing all axes
	 * @param boPlotClientArea
	 *            The bounds of the actual client area
	 *