FastStone Photo Resizer Portable is a great choice for travelers or anyone who takes a lot of pictures on the go, and not just because it runs on almost any Windows machine (XP to 8, server included) without being installed or leaving traces when you remove it, or because it's free (both work for us). But with Photo Resizer Portable on your thumb drive, you can resize, rename, rotate, crop, or convert images, alter colors, and apply text and watermarks from any PC you can access. We tried FastStone Photo Resizer Portable in 64-bit Windows 7.
Since FastStone Photo Resizer Portable is fully portable, you should be sure to extract the zipped download to a memorable location like the desktop. The program's extracted folder has everything it needs, so to move it to your thumb drive or another device, simply drag, copy, or cut and paste the entire folder, insert the drive into any compatible PC, and FastStone Photo Resizer Portable will run normally when you click it. The program's user interface is attractively utilitarian, with tabs for Batch Convert and Batch Rename (though you can do both from either tab by clicking "Use Advanced Options"). The layout is basic and familiar: Browse to images on the left-hand tree view, click "Add" to add them to Photo Resizer's Input List (or Remove, Clear, or Add All) and then select Output Format. We also enabled the Advanced Options and renamed a batch with sequential numbers (you can specify as starting number, too) so by the time we got around to the Batch Rename tab we were familiar with Photo Resizer's speed.
We liked the installed version of FastStone Photo Resizer when we tried it, and we like the portable version, too. Both are free for non-commercial use, so which one you choose depends on your needs. FastStone has you covered in either case.