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
case AttributePackage.CHART_TYPE_OBJECT :
				return createChartTypeObjectFromString( eDataType, initialValue );
			case AttributePackage.DATA_POINT_COMPONENT_TYPE_OBJECT :
				return createDataPointComponentTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.DATA_TYPE_OBJECT :
				return createDataTypeObjectFromString( eDataType, initialValue );
			case AttributePackage.DATE_FORMAT_DETAIL_OBJECT :
				return createDateFormatDetailObjectFromString( eDataType,
						initialValue );
			case AttributePackage.DATE_FORMAT_TYPE_OBJECT :
				return createDateFormatTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.DIRECTION_OBJECT :
				return createDirectionObjectFromString( eDataType, initialValue );
			case AttributePackage.GROUPING_UNIT_TYPE_OBJECT :
				return createGroupingUnitTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.HORIZONTAL_ALIGNMENT_OBJECT :
				return createHorizontalAlignmentObjectFromString( eDataType,
						initialValue );
			case AttributePackage.ID :
				return createIDFromString( eDataType, initialValue );
			case AttributePackage.INTERSECTION_TYPE_OBJECT :
				return createIntersectionTypeObjectFromString( eDataType,
						initialValue );
			case AttributePackage.LEADER_LINE_STYLE_OBJECT :
				return createLeaderLineStyleObjectFromString( eDataType,
						initialValue );
			case AttributePackage.LEGEND_BEHAVIOR_TYPE_OBJECT :