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
* Calls <code>validateXXX</code> for the corresonding classifier of the model.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	protected boolean validate( int classifierID, Object value,
			DiagnosticChain diagnostics, Map context )
	{
		switch ( classifierID )
		{
			case AttributePackage.ACTION_VALUE :
				return validateActionValue( (ActionValue) value,
						diagnostics,
						context );
			case AttributePackage.ANGLE3_D :
				return validateAngle3D( (Angle3D) value, diagnostics, context );
			case AttributePackage.AXIS_ORIGIN :
				return validateAxisOrigin( (AxisOrigin) value,
						diagnostics,
						context );
			case AttributePackage.BOUNDS :
				return validateBounds( (Bounds) value, diagnostics, context );
			case AttributePackage.CALL_BACK_VALUE :
				return validateCallBackValue( (CallBackValue) value,
						diagnostics,
						context );
			case AttributePackage.COLOR_DEFINITION :
				return validateColorDefinition( (ColorDefinition) value,
						diagnostics,
						context );
			case AttributePackage.DATA_POINT :