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/model/attribute/impl/AttributeFactoryImpl.java
return createLegendBehaviorTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.LEGEND_ITEM_TYPE_OBJECT :
				return createLegendItemTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.LINE_DECORATOR_OBJECT :
				return createLineDecoratorObjectFromString( eDataType,
						initialValue );
			case AttributePackage.LINE_STYLE_OBJECT :
				return createLineStyleObjectFromString( eDataType, initialValue );
			case AttributePackage.MARKER_TYPE_OBJECT :
				return createMarkerTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.ORIENTATION_OBJECT :
				return createOrientationObjectFromString( eDataType,
						initialValue );
			case AttributePackage.PERCENTAGE :
				return createPercentageFromString( eDataType, initialValue );
			case AttributePackage.PERCENTAGE_OBJECT :
				return createPercentageObjectFromString( eDataType,
						initialValue );
			case AttributePackage.POSITION_OBJECT :
				return createPositionObjectFromString( eDataType, initialValue );
			case AttributePackage.RGB_VALUE :
				return createRGBValueFromString( eDataType, initialValue );
			case AttributePackage.RGB_VALUE_OBJECT :
				return createRGBValueObjectFromString( eDataType, initialValue );
			case AttributePackage.RISER_TYPE_OBJECT :
				return createRiserTypeObjectFromString( eDataType, initialValue );
			case AttributePackage.RULE_TYPE_OBJECT :