Image Resize Options

I have created a form for people to upload images and create a post for a photo contest. I would like to be able to ensure people can't upload huge images and was wondering the best way to handle this. I have a few ideas but don't know if they are possbile.

1) I have http://wordpress.org/support/plugin/imsanity installed. Is there a hook or something I can do to enable Imsanity to intercept and process the file upload?

2) We are holding the generated posts for approval and Imsanity has a bulk image re-size option. We can use this to resize the images before approval but the image size has been placed in the post. Is there a way to prevent the size from being placed in the post.

3) Is there a way to add custom sizes created in functions.php to the dropdown in the content template options.

4) Are there any other options I haven't thought of.

Many Thanks

I just implemented a pretty straight forward approach to resize images uploaded with Gravity Forms using Wordpress 3.5 image manipulation. Here's the code:

//resize images uploaded to Gravity Form 3.  Replace 3 below with form ID
add_action("gform_after_submission_3", "gf_resize_images", 10, 2);
function gf_resize_images($entry, $form)
{
	//replace 14 with field ID of upload field
	$url =  $entry[14];
	$parsed_url = parse_url($url);
	$path = $_SERVER['DOCUMENT_ROOT'] . $parsed_url['path'];
	$image = wp_get_image_editor($path);
	if ( ! is_wp_error( $image ) )
	{
		//replace 640,480 with desired dimensions.  false indicates not to crop image.
		$result = $image->resize( 640,480,false );
		$result = $image->save($path);
	}
}

Works like a charm on all forms whether they create a post or not!

Hi Trestian, its workin too in Wordpress 3.4??

This image resizing solution works great from desktop. Thank you very much for the code.

For some reason though, the images are not resized when you are using the jetpack mobile theme addon. Also - it seems like the file uploader is having a hard time distinguishing between JPG & jpg.