I've been uploading a lot of pictures lately, to Flickr, Facebook, Etsy, etc. Almost all my pictures are from my digital camera and they're fairly large files. I resize them in batches using Adobe Photoshop 7. It has saved me a lot of time. I use the web gallery function. It will resize your images automatically, create thumbnails, even a html document displaying everything if that is also what you need. Here's how I do it step by step.
1. Open up Adobe Photoshop 7
2. Go to File > Automate > Web Photo Gallery
3. A dialog box will pop up. Please see the picture below. Under FOLDERS, you will see BROWSE and DESTINATION. Click BROWSE and locate the folder that has all of the images you want resized.
4. Now click on DESTINATION, create a new folder. This new folder is where your new resized photos and html documents will appear.
5. The dropdown box next to OPTIONS should be showing BANNER by default. For SITE NAME just give it a title if you want the html documents to have one or you can just leave it the way it is.
6. Click on the dropdown box and go to the next option LARGE IMAGE. There are several steps here.
a) Make sure the box next to RESIZE IMAGES is checked.
b) By default, MEDIUM is selected and your resized images are set to be 350 pixels in width or height depending on what you choose under CONSTRAIN. You can change the setting to whatever you'd like. I usually keep it under 500 pixels.
c) Under CONSTRAIN, you can choose either to have your resized images a certain width or height. By selecting BOTH though, your image will be a perfect square. I recommend either WIDTH or HEIGHT. You don't want to have distorted images in the end.
d) JPEG QUALITY is totally up to you. The higher the value the better the quality. Keep in mind though, the file size will be bigger too.
e) The rest of the settings are pretty much self explanatory. I won't go into details here.
After everything is set to the way you want, click OK. Wal-lah, the computer will do the rest of the work. Look for the resized images in your destination folder.