Last week my wife uploaded some pictures taken from her camera to her online flickr account. Soon the account got filled up to its free 100 MB per month limit. She could have uploaded many more pictures if they had been re-sized before uploading. In my search for a simple and inexpensive tool, I found a Microsoft Power Toy called ImageResizer which can resize multiple files in one operation. You can download it from here.
This tool is incredibly simple. Just explore to the folder on your desktop where the images are. Select all files that you want to resize, right-click and click Resize Pictures menu item. In the Resize Pictures screen, select the size to which you want to resize the pictures to. Thats it.
How it helped
In my tests an original 1.2 MB jpg file was resized into a 800×600 image of 60 kb. Wow..now 20 times more pics can be uploaded with same 100 MB per month limit.