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/util/AttributeValidator.java
context );
			case AttributePackage.CHART_DIMENSION_OBJECT :
				return validateChartDimensionObject( (ChartDimension) value,
						diagnostics,
						context );
			case AttributePackage.CHART_TYPE_OBJECT :
				return validateChartTypeObject( (ChartType) value,
						diagnostics,
						context );
			case AttributePackage.DATA_POINT_COMPONENT_TYPE_OBJECT :
				return validateDataPointComponentTypeObject( (DataPointComponentType) value,
						diagnostics,
						context );
			case AttributePackage.DATA_TYPE_OBJECT :
				return validateDataTypeObject( (DataType) value,
						diagnostics,
						context );
			case AttributePackage.DATE_FORMAT_DETAIL_OBJECT :
				return validateDateFormatDetailObject( (DateFormatDetail) value,
						diagnostics,
						context );
			case AttributePackage.DATE_FORMAT_TYPE_OBJECT :
				return validateDateFormatTypeObject( (DateFormatType) value,
						diagnostics,
						context );
			case AttributePackage.DIRECTION_OBJECT :
				return validateDirectionObject( (Direction) value,
						diagnostics,
						context );
			case AttributePackage.GROUPING_UNIT_TYPE_OBJECT :