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/AttributePackage.java
/**
	 * The meta object id for the '<em>Legend Item Type Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LegendItemType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLegendItemTypeObject()
	 * @generated
	 */
	int LEGEND_ITEM_TYPE_OBJECT = 86;
	/**
	 * The meta object id for the '<em>Line Decorator Object</em>' data type.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LineDecorator
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLineDecoratorObject()
	 * @generated
	 */
	int LINE_DECORATOR_OBJECT = 87;
	/**
	 * The meta object id for the '<em>Line Style Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LineStyle
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLineStyleObject()
	 * @generated
	 */
	int LINE_STYLE_OBJECT = 88;
	/**
	 * The meta object id for the '<em>Marker Type Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.MarkerType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getMarkerTypeObject()