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 '{@link org.eclipse.birt.chart.model.attribute.impl.ScriptValueImpl <em>Script Value</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.ScriptValueImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getScriptValue()
	 * @generated
	 */
	int SCRIPT_VALUE = 27;
	/**
	 * The feature id for the '<em><b>Script</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int SCRIPT_VALUE__SCRIPT = ACTION_VALUE_FEATURE_COUNT + 0;
	/**
	 * The number of structural features of the the '<em>Script Value</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int SCRIPT_VALUE_FEATURE_COUNT = ACTION_VALUE_FEATURE_COUNT + 1;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.SeriesValueImpl <em>Series Value</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.SeriesValueImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getSeriesValue()
	 * @generated
	 */
	int SERIES_VALUE = 28;