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
* @param ax
	 * @param iWhatToDraw
	 * 
	 * @throws RenderingException
	 */
	public final void renderEachAxis( IPrimitiveRenderer ipr, Plot pl,
			OneAxis ax, int iWhatToDraw ) throws ChartException
	{
		final RunTimeContext rtc = getRunTimeContext( );
		final Axis axModel = ax.getModelAxis( );
		final PlotWithAxes pwa = (PlotWithAxes) getComputations( );
		final Insets insCA = pwa.getAxes( ).getInsets( );
		final ScriptHandler sh = getRunTimeContext( ).getScriptHandler( );
		double dLocation = ax.getAxisCoordinate( );
		double dAngleInDegrees = ax.getLabel( )
				.getCaption( )
				.getFont( )
				.getRotation( );
		AutoScale sc = ax.getScale( );
		IntersectionValue iv = ax.getIntersectionValue( );
		int iMajorTickStyle = ax.getGrid( ).getTickStyle( IConstants.MAJOR );
		int iMinorTickStyle = ax.getGrid( ).getTickStyle( IConstants.MINOR );
		int iLabelLocation = ax.getLabelPosition( );
		int iOrientation = ax.getOrientation( );
		Label la = ax.getLabel( );
		final IDisplayServer xs = this.getDevice( ).getDisplayServer( );
		double[] daEndPoints = sc.getEndPoints( );
		double[] da = sc.getTickCordinates( );
		double[] daMinor = sc.getMinorCoordinates( ax.getGrid( )
				.getMinorCountPerMajor( ) );