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
int BOUNDS__HEIGHT = 3;
	/**
	 * The number of structural features of the the '<em>Bounds</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int BOUNDS_FEATURE_COUNT = 4;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.CallBackValueImpl <em>Call Back Value</em>}' class.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.CallBackValueImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getCallBackValue()
	 * @generated
	 */
	int CALL_BACK_VALUE = 4;
	/**
	 * The feature id for the '<em><b>Identifier</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int CALL_BACK_VALUE__IDENTIFIER = ACTION_VALUE_FEATURE_COUNT + 0;
	/**
	 * The number of structural features of the the '<em>Call Back Value</em>' class.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated