Optimizing images would always be a tedious task if you are not utilizing a good image processing tool. Certain resizing tools promise that the output images to be optimized, but what they really do is to reduce the clarity of the image and hence its size. But there are certain tools like RIOT, which goes into depths of resampling to perform the actual image optimization.
Optimization with RIOT is very simple. Drag-n-drop the image to be processed onto RIOT and it does everything for you. If you are not satisfied with the default settings, tweak the options available to fine tune further. Use the Resize/Resample option to change the image dimensions and quality.
RIOT Resample
Making RIOT Portable:
Use the method mentioned in this post, to make this application portable so that you can run it directly from your USB Thumb drive.
Features:
- Save and optimize JPEG, GIF and PNG with a simple, clean user interface
- Compress files to desired filesize
- Processing is super fast
- Option to remove metadata (Comments, IPTC, Adobe XMP, EXIF profiles, ICC profiles)
- Resize image by using well known resample filters (ex: Lanczos3, Catmull Rom, Bicubic, and others)
- Adaptive logarithmic tone mapping algorithm (Drago) used for HDR images
- Free and Portable!!!
Download RIOT : 
More details at RIOT Homepage
