I solve like this :
placemark.options.set('iconImageHref', 'http:www.example.com/images/1.png');
placemark.options.set('iconImageOffset', [-1, -30]);
placemark.options.set('iconImageSize', [28,29]);
placemark.options.set('iconShadowImageHref', 'http:www.example.com/images/2.png');
placemark.options.set('iconShadowImageOffset', [2, -12]);
placemark.options.set('iconShadowImageSize', [29, 7]);