ArcVieh

You can select images from media Library in the Widgets backend that will be shown on your Page. You can enter a size for the images.
The thumb-images will be linked to the full-sized-image. 
Requieres PHP 5!

Media Images Widget

Requieres PHP 5! You can select images from media Library in the Widgets backend that will be shown on your Page.

brasofilo

The plugin adds a meta box where you can upload or select an image from your media library.
After selection, the default Link Image field is populated with the image URL and a preview is available in the meta box.
The plugin also adds a Thumbnail column in the page /wp-admin/link-manager.php
Inspired by <a href="http://wordpress.stackexchange.com/questions/44902/uploading-images-for-links" rel="nofollow ugc">this question</a> in WordPress Answers.
<h4>Localizations</h4>
Português & Español

Featured Link Image

Add a meta box in the Links add/edit page for easy uploading/inserting images in your bookmarks.

Media Images Widget vs Featured Link Image