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
instanceValue );
			case AttributePackage.LINE_DECORATOR_OBJECT :
				return convertLineDecoratorObjectToString( eDataType,
						instanceValue );
			case AttributePackage.LINE_STYLE_OBJECT :
				return convertLineStyleObjectToString( eDataType, instanceValue );
			case AttributePackage.MARKER_TYPE_OBJECT :
				return convertMarkerTypeObjectToString( eDataType,
						instanceValue );
			case AttributePackage.ORIENTATION_OBJECT :
				return convertOrientationObjectToString( eDataType,
						instanceValue );
			case AttributePackage.PERCENTAGE :
				return convertPercentageToString( eDataType, instanceValue );
			case AttributePackage.PERCENTAGE_OBJECT :
				return convertPercentageObjectToString( eDataType,
						instanceValue );
			case AttributePackage.POSITION_OBJECT :
				return convertPositionObjectToString( eDataType, instanceValue );
			case AttributePackage.RGB_VALUE :
				return convertRGBValueToString( eDataType, instanceValue );
			case AttributePackage.RGB_VALUE_OBJECT :
				return convertRGBValueObjectToString( eDataType, instanceValue );
			case AttributePackage.RISER_TYPE_OBJECT :
				return convertRiserTypeObjectToString( eDataType, instanceValue );
			case AttributePackage.RULE_TYPE_OBJECT :
				return convertRuleTypeObjectToString( eDataType, instanceValue );
			case AttributePackage.SCALE_UNIT_TYPE_OBJECT :
				return convertScaleUnitTypeObjectToString( eDataType,
						instanceValue );