FastStone Photo Resizer is designed to make resizing of large numbers of photos on the move as easy as possible.
If you're a design professional or produce presentations on a regular basis, you'll find this program useful especially if you travel around a lot. You can perform several basic functions in addition to resizing such as rotating, cutting and pasting, colour alterations and of course adjust the brightness and contrast of your images. In addition, once resized, you can add text and watermarks to images although the text styles and formats are limited. Of course, this is nothing special for an image resizer but the big bonus is that it can be run directly from a USB stick in which case it doesn't need installing - perfect if you are in a hurry.
The interface is very easy to use and supports the dragging and dropping of images into the program which speeds up conversions of huge batches significantly compared to browsing to each file. It supports a decent amount of formats including the relatively rare JPEG2000 format which is unusual for any type of imaging utility. The batch renaming and resizing utility also saves you work and time (and the risk of duplicated images) by automatically renumbering adjusted images in sequential order.
This is an excellent portable image resizer and if you're looking for something in this area which is free, fast and simple, you need look no further.