XnConvert!

ImageMagick is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (about 100) including GIF, JPEG, JPEG-2000, PNG, PDF, PhotoCD, TIFF, and DPX. Use ImageMagick to translate, flip, mirror, rotate, scale, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves. ImageMagick is free software delivered as a ready-to-run binary distribution or as source code that you can freely use, copy, modify, and distribute. Its license is compatible with the GPL. It runs on all major operating systems. The functionality of ImageMagick is typically utilized from the command line or you can use the features from programs written in your favorite programming language. Choose from these interfaces: MagickCore (C), MagickWand (C), ChMagick (Ch), Magick++ (C++), JMagick (Java), L-Magick (Lisp), PascalMagick (Pascal), PerlMagick (Perl), MagickWand for PHP (PHP), PythonMagick (Python), RMagick (Ruby), or TclMagick (Tcl/TK). With a language interface, use ImageMagick to modify or create images automagically and dynamically. »

Saving images for web/email/other media with the best compression ratio and quality is a difficult task if you don’t have the right tools. Choosing the right format then choosing the right parameters are the key factors of smaller files. Previewing the resulting image and the projected filesize will help the user choose the best settings. This kind of image optimization software is often called “Save for web”.

-Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs-No image quality is lost — only file size-Converts JPG, GIF, TIFF, and BMP files to PNG-Ultra-configurable

Phatch = Photo & Batch! Phatch is a simple to use cross-platform GUI Photo Batch Processor which handles all popular image formats and can duplicate (sub)folder hierarchies. Phatch can batch resize, rotate, rename, ... and more in minutes instead of hours or days if you do it manually. Phatch will also support a console version in the future to batch photos on web servers.

TinyPNG uses smart lossy compression techniques to reduce the file size of your PNG files. By selectively decreasing the number of colours in the image, fewer bytes are required to store the data. The effect is nearly invisible but it makes a very large difference in file size!

XnShell is a free File Explorer extension that installs a number of image-related tools in the right-click context menu, including a thumbnail preview, image conversion to a wide variety of formats, image resizing, editing image IPTC metadata, uploading to ImageShack, and other functions.

Convert and Rename images in batch mode

Image Tuner is a free software for batch resizing, converting, watermarking and renaming your digital photos and images from more than 20 image formats to JPEG, BMP, PNG, TIFF and GIF formats. The program will help you to prepare your digital photos to upload and publish them in the Internet or send via e-mail.

Converseen is an open source batch image resizer and conversion tool written in C++ with the powerful Qt4 libraries.

Imaging is a Collection of Image Related Tools (Image Viewer, Image Converter, Image Resizer, Image Optimizer, etc).

ImBatch is a batch image processor with a nice graphical user interface. It will allow you to edit multiple image files at the click of a button by using scripts. The script will be created by combining Tasks. ImBatch can batch resize and convert images in minutes instead of hours or days if you do it manually. It handles all popular image formats: BMP, DIB, RLE, TIF, TIFF, FAX, G3N, G3F, XIF, GIF, JPG, JPEG, JPE, JIF, PCX, PNG, TGA, TARGA, VDA, ICB, VST, PIX, PXM, PPM, PGM, PBM, WBMP, JP2, J2K, JPC, J2C, DCX, DAT, PSD, WDP, HDP. And it is absolutely FREE. »

Image Resizer for Windows is a utility that lets you resize one or more selected image files directly from Windows Explorer by right-clicking.

Light Image Resizer, previously called VSO Image Resizer, is a shareware resize image software. With it you can create e-mail friendly versions of your images, load them faster, move them easily from folder to folder, change their format, edit large numbers of image files/batch image resize and thus save space on your hard drive. Using high resolution 1600x1200 for creating wallpaper or file-sharing you can save your memory. Light Image Resizer can also change file names using a template and you can add your own watermark with transparency support. Light Image Resizer is integrated into the Windows explorer shell, right click on your pictures and start working on your pictures ! »

GraphicsMagick is the swiss army knife of image processing. Comprised of 282K physical lines (according to David A. Wheelers SLOCCount) of source code in the base package (or 952K including 3rd party libraries) it provides a robust and efficient collection of tools and libraries which support reading, writing, and manipulating an image in over 88 major formats including important formats like DPX, GIF, JPEG, JPEG-2000, PNG, PDF, PNM, and TIFF.