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
* Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.TextAlignment#getVerticalAlignment <em>Vertical Alignment</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Vertical Alignment</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TextAlignment#getVerticalAlignment()
	 * @see #getTextAlignment()
	 * @generated
	 */
	EAttribute getTextAlignment_VerticalAlignment( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.TooltipValue <em>Tooltip Value</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for class '<em>Tooltip Value</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TooltipValue
	 * @generated
	 */
	EClass getTooltipValue( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.TooltipValue#getText <em>Text</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Text</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TooltipValue#getText()
	 * @see #getTooltipValue()
	 * @generated
	 */
	EAttribute getTooltipValue_Text( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.TooltipValue#getDelay <em>Delay</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Delay</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TooltipValue#getDelay()