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
String sText = null;
		int iDimension = pwa.getDimension( );
		double dSeriesThickness = pwa.getSeriesThickness( );
		final NumberDataElement nde = NumberDataElementImpl.create( 0 );
		final FormatSpecifier fs = ax.getModelAxis( ).getFormatSpecifier( );
		final double dStaggeredLabelOffset = sc.computeStaggeredAxisLabelOffset( xs,
				la,
				iOrientation );
		final boolean bAxisLabelStaggered = sc.isAxisLabelStaggered( );
		DecimalFormat df = null;
		LineAttributes lia = ax.getLineAttributes( );
		LineAttributes liaMajorTick = ax.getGrid( )
				.getTickAttributes( IConstants.MAJOR );
		LineAttributes liaMinorTick = ax.getGrid( )
				.getTickAttributes( IConstants.MINOR );
		if ( !lia.isSetVisible( ) )
		{
			throw new ChartException( ChartEnginePlugin.ID,
					ChartException.RENDERING,
					"exception.unset.axis.visibility", 
					ResourceBundle.getBundle( Messages.ENGINE,
							getRunTimeContext( ).getLocale( ) ) );
		}
		final boolean bRenderAxisLabels = ( ( iWhatToDraw & IConstants.LABELS ) == IConstants.LABELS && la.isVisible( ) );
		final boolean bRenderAxisTitle = ( ( iWhatToDraw & IConstants.LABELS ) == IConstants.LABELS );
		Location lo = LocationImpl.create( 0, 0 );
		final TransformationEvent trae = (TransformationEvent) ( (EventObjectCache) ipr ).getEventObject( StructureSource.createAxis( axModel ),
				TransformationEvent.class );
		final TextRenderEvent tre = (TextRenderEvent) ( (EventObjectCache) ipr ).getEventObject( StructureSource.createAxis( axModel ),
				TextRenderEvent.class );