Abrar Ahmed

This plugin is particularly designed for developers so that they can easily upload images via URL.
Features of this plugin: 
1. You can give URL to this plugin then this will upload the image to WP and will return attachment ID. 
2. You can give the same URL multiple times but it will not upload an image each time, it will upload an image once and will return attachment ID each time when it is called. 
3. If image URL is change or size of the image on URL is different then just on that condition image will be uploaded to WordPress
It has some more functions too that will help developers for getting details about image and size as well.
<h3>Arbitrary section</h3>
The following features of this plugin are going to be defined for developer understandings.
<h3>A brief Markdown Example</h3>
Unordered list:
<ul>
<li>Function iUploadImageByURL This function is the basic function that can be used while upload image from URL. It will return Attachment_ID after creating an attachment from image URL. Image from URL will be uploaded once if URL and size of the image are same. If the same URL with the same size of the image given then already created attachment of that image will be uploaded.</li>
<li>Function iGetFileSize This function can be used to get the size of the image from URL.</li>
<li>Function sFormatSize This function will return measurement format size of the image.</li>
</ul>

URL Image Uploader

This function is a tool for developers to help them upload images from URL to the WordPress site.

Samuel Wood (Otto)

Normally when you upload an image to a WordPress site, it creates several differently sized versions of the image automatically. Themes can define custom image sizes as well, increasing the amount of images generated on your server.
This plugin changes the way WordPress creates images to make it generate the images only when they are actually used somewhere, on the fly. Images created thusly will be saved in the normal upload directories, for later fast sending by the webserver. The result is that space is saved (since images are only created when needed), and uploading images is much faster (since it’s not generating the images on upload anymore).
“Pretty” permalinks must be enabled for this plugin to function.
Note: This plugin does not work on multisite setups, due to the way WordPress handles file serving in such situations (with ms-files.php).
Want regular updates? Become a fan of my sites on Facebook! 
http://www.facebook.com/apps/application.php?id=116002660893 
http://www.facebook.com/ottopress
Or follow my sites on Twitter! 
http://twitter.com/ottodestruct

Dynamic Image Resizer

Make your images change sizes dynamically.

URL Image Uploader vs Dynamic Image Resizer