I use plugin wp-type, there I can make costum pages, this plugin have function to display image in page or post, but fom me this function not work, image was still not resized. Maybe are some better solution to resize proportionaly images in pages/posts ?
<?php echo(types_render_field("product_image", array("alt"=>"Product image",
"width"=>"300","height"=>"200","proportional"=>"true"))); ?>
You can use this plugin to achieve your requirement, I have used in many of my projects and it worked perfectly. Here is the plugin link http://austinmatzko.com/wordpress-plugins/filosofo-custom-image-sizes/