I have tested lot of free batch image editing tools, but I feel this one is great. It is called “FastStone Image Viewer.” It is powerful, fast, has standalone alone version, and moreover it is completely free.
“It has a nice array of features that include image viewing, management, comparison, red-eye removal, emailing, resizing, cropping, retouching and color adjustments. Its innovative but intuitive full-screen mode provides quick access to EXIF information, thumbnail browser and major functionalities via hidden toolbars that pop up when your mouse touches the four edges of the screen. Other features include a high quality magnifier and a musical slideshow with 150+ transitional effects, as well as lossless JPEG transitions, drop shadow effects, image annotation, scanner support, histogram and much more. It supports all major graphic formats (BMP, JPEG, JPEG 2000, animated GIF, PNG, PCX, PSD, EPS, TIFF, WMF, ICO and TGA) and popular digital camera RAW formats (CRW, CR2, NEF, PEF, RAF, MRW, ORF, SRF, ARW, SR2, RW2 and DNG).”
From the above description by FastStone, you can understand how rich it is in functionality. You can do almost all image related processes using this software. It is portable, so you can carry it in a USB stick too. No installation necessary.
Below is the procedure to batch watermark your photos / images using this free software. You can add a png file with transparent background or just text to watermark your images.
Select the directory on the left side where all you images are and on the right side you can see all the images. Select all the images by pressing pressing Ctrl+A from keyboard. Unselect any folder by pressing Ctrl button and clicking on the folder icon.
Then, click Tools>Batch Convert Selected Images. You can also press F3 to invoke the same. On the right bottom you can see a button “Advanced Options.”
Select it and click the tab “Text” if you want to watermark you images with a text or select “Watermark” tab if you want to watermark with a transparent png file. Choose the options and fine tune the logo / text to your liking.
Select the output folder and click convert. You are done!
Visit the product page at: http://www.faststone.org/FSViewerDetail.htm