WPsites

Resize your images before they are uploaded to your website (server), no need to use image editing software. Drag+drop images from your digital camera to WordPress. This plugin works best in HTML5 compatible web browsers such as Chrome or Firefox.
If your web browser does not support HTML5 then this plugin will swap your image uploader runtime to the Adobe Flash version which makes sure the resize function works across more web browsers. The side effect to this is drag+drop will be disabled since this is not supported in Flash (everything works in HTML5 compatible browsers). If you experience issues or drag+drop is more important to you than resizing images then you can disable the Flash override in your settings -> media.
This plugin does not work on the iPhone or iPad.
This plugin removes the upload file size limit and turns on the resize function.
Once this plugin is enabled your images will be resized in the browser before being uploaded to your website (server).
This plugin adds an additional setting to your settings -> media page that allows you to specify the image quality when being resized. The quality value can range from 1-100. The higher the quality the larger the file size. The default value is 80 which reduces the file size whilst still maintaining a decent quality image. You can also set the resize dimensions for this plugin here to, if you weren’t happy inheriting the default large image size settings.
<ul>
<li>Less bandwidth used for your host when uploading your images</li>
<li>No more massive images uploaded to your site for users to sit waiting to view/download</li>
<li>You can drag images right off your digital camera onto the WordPress uploader, getting them online in a flash.</li>
</ul>
If you want to force the resized image width/height, overriding the media settings (making it so multisite users cannot change this value etc) you can do this in wp-config.php by setting two constants:
define( ‘RIBU_RESIZE_WIDTH’, 1000 ); //1000 px wide 
define( ‘RIBU_RESIZE_HEIGHT’, 900 ); //900 px high
define( ‘RIBU_RESIZE_QUALITY’, 75 ); //0-100, 100 being high quality 
defined( ‘RIBU_MAX_UPLOAD_SIZE’ ‘2097152b’ ) ); //size in bytes
To work, any settings added to your wp-config.php file should be done above the line that reads: 
/* That’s all, stop editing! Happy blogging. */
Find the plugin on github: https://github.com/WPsites/Resize-images-before-upload
<h3>Contributors</h3>
Simon Dunton – http://www.wpsites.co.uk

Resize images before upload

Upon searching the Wordpress repository, it's clear that every plugin that resizes images for you is a paid service, with one exception, THIS plugin! By resizing the imaegs on our website, we've been able to drastically reduce traffic and server load. The benefits become even more apparent as we continue to grow. Thanks for this brilliant plugin!

Brilliant Plugin

Automatically resizes your images right in your browser, before uploading.

llvasconcellos

*** ATENTION ***
Due to modifications on the Media Library the plugin only works with the “UPLOAD NEW MEDIA” form located under Media -> Add New menu entry on the left menu. If you click direct on Media and use the Add New button of MEDIA LIBRARY the plugin will not be executed.
I filled a bug report here: 
https://core.trac.wordpress.org/ticket/39492
With this plugin you can use High Resolution images directly from your camera to WordPress without using any additional software to resize them. You only have to use a HTML5 capable browser.
<ul>
<li>Works with Drag & Drop!</li>
</ul>
Exemple of capable browsers are: Chrome, Firefox, Opera, IOS e Android.
It will add extra media settings at SETTINGS -> MEDIA where you can specify resized JPG quality and maximum width and height for each uploaded image.
Brought to you by DevHouse – Internet Software Development House: http://www.devhouse.com.br
Com este plugin você pode usar diretamente as imagens em alta resolução diretamente da sua câmera digital diretamente para o WordPress sem a necessidade de passar por softwares adicionais para redimensioná-las. Basta ter um browser atualizado.
<ul>
<li>Funciona com Drag & Drop!</li>
</ul>
Exemplos de Browsers são: Chrome, Firefox, Opera, IOS e Android.
Ele adicionará configurações adicionais em CONFIGURAÇÕES -> MÍDIA onde você pode especificar a qualidade do JPG redimensionado e largura e altura máximas para cada imagem enviada.
Trazido para você por DevHouse – Internet Software Development House: http://www.devhouse.com.br

Client Side Image Resize

Uses HTML5 to resize large images before uploading to server.

Resize images before upload vs Client Side Image Resize