Bug 149922 Image builder - URI and file source type are treated as same
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/ImageHandle.java
*/
	public String getTypeExpression( )
	{
		if ( DesignChoiceConstants.IMAGE_REF_TYPE_EXPR
				.equalsIgnoreCase( getSource( ) ) )
		{
			return getStringProperty( ImageItem.TYPE_EXPR_PROP );
		}
		return null;
	}
	/**
	 * Returns the value expression of the image if the image source type is
	 * <code>IMAGE_REF_TYPE_EXPR</code>.
	 * 
	 * @return the value expression, if the image source type is
	 *         <code>IMAGE_REF_TYPE_EXPR</code>. Otherwise, return
	 *         <code>null</code>.
	 */
	public String getValueExpression( )
	{
		if ( DesignChoiceConstants.IMAGE_REF_TYPE_EXPR
				.equalsIgnoreCase( getSource( ) ) )
		{
			return getStringProperty( ImageItem.VALUE_EXPR_PROP );
		}
		return null;
	}
	/**
	 * Returns the embedded image name that this image refers, if the image
	 * source type is <code>IMAGE_REF_TYPE_EMBED</code>. This is not the same