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.LINE_STYLE :
				return validateLineStyle( (Object) value, diagnostics, context );
			case AttributePackage.MARKER_TYPE :
				return validateMarkerType( (Object) value, diagnostics, context );
			case AttributePackage.ORIENTATION :
				return validateOrientation( (Object) value,
						diagnostics,
						context );
			case AttributePackage.POSITION :
				return validatePosition( (Object) value, diagnostics, context );
			case AttributePackage.RISER_TYPE :
				return validateRiserType( (Object) value, diagnostics, context );
			case AttributePackage.RULE_TYPE :
				return validateRuleType( (Object) value, diagnostics, context );
			case AttributePackage.SCALE_UNIT_TYPE :
				return validateScaleUnitType( (Object) value,
						diagnostics,
						context );
			case AttributePackage.SORT_OPTION :
				return validateSortOption( (Object) value, diagnostics, context );
			case AttributePackage.STRETCH :
				return validateStretch( (Object) value, diagnostics, context );
			case AttributePackage.STYLED_COMPONENT :
				return validateStyledComponent( (Object) value,
						diagnostics,
						context );
			case AttributePackage.TICK_STYLE :
				return validateTickStyle( (Object) value, diagnostics, context );
			case AttributePackage.TRIGGER_CONDITION :