* Breaking News *
I have no plans of further developing this plugin since the plugin Scissors has that ability too, and much more.
Here is the presentation of the plugin “Resize at Upload”. I’ve read many requests for a plugin like this and I was looking around for something like this too. Because I couldn’t find any, I decided to write one myself.
You can download the plugin here: http://wordpress.org/extend/plugins/resize-at-upload/
As you can see above, there are two settings. One setting is if you want to resize. Set this one to “no” if you don’t want to resize (you don’t have to deactivate the plugin in this case). Maybe in a later version I will include a selection option in the upload area to activate/deactivate resizing.
The other option is the max width. In my theme I use images of 672px width. So I changed this field into 672 and every image (JPG, GIF or PNG) will be resized when it is uploaded.
Keep in mind, there is no backup or original file kept with the original sizes. The file you are uploading, is affected and resized.
The plugin requires PHP4 (at least), and is tested with WordPress 2.6 and higher. There is no problem to use the multiple upload option, each image is resized.
Keep in mind that WordPress will show images width max 500px if there is no variable set. Maybe from WordPress 2.7 it will be different but the current version (2.6 and subversions) needs a variable to show images larger. This plugin will not change that nor help you with this. That’s your problem to solve in your theme 
Addition Nov, 19th 2008: EXIF data will be lost. I’m not sure if in the future there will be a solution for this.
Addition Jan, 13th 2009: Daniel Mores liked the plugin and he got some ideas which could make the plugin better, so he altered some code of my plugin and is now publishing it via his website. The contribution of Daniel is that it is also possible to set a max height so that portrait images will be reduced as well. His release is not an official update but if you prefer his plugin, you are able to use his version. When I will improve my plugin somewhere in the future, I will take his option as an improvement so the use of this plugin on your website will not be disturbed. But at the moment I prefer to keep my plugin the way it is.
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Contributions/stolen code 
For this plugin I use a class from Jacob Wyke (www.redvodkajelly.com) and parts of the plugin Upload+ from Paolo Tresso / Pixline (http://pixline.net).
Na een jarenlange ervaring in programmeren en webdesign wordt deze blog gevuld met artikelen die gerelateerd zijn aan internet. Daarnaast bij vlagen een column of een mooie foto.
Hey, this is a great plugin!
Thnx!
Thank you so much for this plugin.
You saved my day.
Hi, I am just wondering if it’s possible to make it resize the max height as well?
thank you.
No, the purpose of this plugin is to resize in width only, to avoid breaking the layout of the used theme. If you want to resize the height to a given width you can change the source code or use another plugin where you can resize things. A cool one can be found here: http://stephanreiter.info/2008/10/wordpress-plugin-scissors/
hi there. how does this plugin affect EXIF data?
I was just wondering as all images I upload that are automatically resized by this plugin, have no EXIF data afterwards. I have no idea if this is a problem with this plugin, or with my server configuration, so please give me soem advise. If you want to see what I am trying to implement, its this plugin which shows EXIf meta data: http://didier.lorphelin.free.fr/blog/index.php/wordpress/lameda/
please give me some advise
EXIF data will be removed. Maybe in a next version I’ll try to keep the information or maybe I can return it as metadata.
did you have a look at lameda plugin I linked above? it seems it can also get metadata… is there any way I could show info about the picture after it has been resized? OR is all that info lost?
All data is lost. The plugin creates a new image with the desired size and it will put the original picture in it. After that, the original file is deleted. So there is no EXIF data left.
I assume it is possible to first retreive the EXIF from the original and store it in the metadata for further use. Or to put it in the new file, anyhow. But at the moment the only purpose of the plugin is to resize it, not to manage it
If I once will update the plugin, I will have a look at this subject. Till then I recommend to keep the original file or to resize it in Photoshop before uploading and in Photoshop keep the EXIF.
Thank you for creating this plugin. Can you tell me if this maintains the aspect ratio after resize?
Yes, it will. You could try it off course
Thanks so much for this plug-in. It is the only one that is compatible with WordPress 2.6.5 that I know!
It does exactly what is needed — without storing the full-size picture on the server (which would take up too much of my hosting space). Highly Recommended!
Wow, what a nice surprise to get a plugin that’s powerful yet totally simple. No frills, it just does what it needs to do.
Awesome. Now my clients won’t fill up their webspace with useless bits and bytes, and lightbox windows won’t span 5 screens
Where can I donate?
A nice comment like yours is the best donation
Okay, now my client is bugging me about too-large images, but only when she uploads portrait-mode photos.
I’ll try to get your plugin to take a height parameter as well and resize it to a max height.
The other plugins you mentioned are way too complicated and require user input during the uploading process … no match for your plugin’s ease of use.
If anyone wants to set a max height -> http://www.mores.cc/better-resize-at-upload
Anton … all credits are still intact, I just increased the version number to 0.9.1. and updated the screenshots.
It’s not in the SVN, I didn’t rename it, I didn’t remove your copyright and I didn’t put myself as the author …. just added my name to the thank-you-list
You may want to incorporate the additions in your next release, maybe fine-tune the options so that maxheight is turn-offable.
Cheers, Daniel
I’ll take a look next weekend
Hey there.
I fixed the plugin – it won’t exceed either height or width.
And I changed the name since I didn’t think it was better, it’s just got one option plus.
So: http://wordpress.org/extend/plugins/resize-at-upload-plus/
Great plugin, does exactly what I was looking for (using the modified version though). However, I found the resized images too ugly, especially if the image is not a photograph but a “rasterized vector image” (you got my point). The results can be made much better by modifying a single line of Jacob Wyke’s class, namely changing the function “imagecopyresized” to “imagecopyresampled” (same arguments).
Now I ask, was this not made yet because of any specific reasons, maybe license? For now, I’ll just have to keep modifying the class.
Good point, I’ll have a look at it
Might be a compatibility issue. imagecopyresampled is available in gd2+ only.
Good point, I’ll have a look at that too
The use of Imagecopyresampled is indeed an improvement.
Hi,
Your plugin works fine, but ..
is it possible to upload only the resized image and not
the (thumbnail) images 150×150 and 300×225
thanks,
Albert
No, that is not the purpose of the plugin. Creating thumbs is a process of WordPress and is not affected by resizing the original photo.
Maybe there are plugins available that do what you want
i think that this is useful, but much more useful would be a plugin that resize the thumbnail because, when the image is huge, you want to show a tiny thumbnail linked to the full image to see all the details.
THanks
You just described standard WordPress technology. You don’t need plugins for that.
Exactly what I needed – thanks.
They really should build this into the core – only 1 out of 100 people wants to display the full size image.