Resizing a hundred photos one by one in Paint is one of those tasks you do once and immediately look for a better way. These free tools let you convert, compress, or watermark entire folders of images in a single step.
Short Answer: IrfanView (free) is the fastest tool for batch converting and resizing images on Windows — select a folder, pick an output format, and it processes everything at once. For watermarking, use FastStone Photo Resizer or XnConvert — both free, both handle batches of hundreds of images.
Tool 1: IrfanView — Best for Batch Conversion and Resize
IrfanView is a lightweight image viewer that most people overlook as a batch processor. It’s been around since 1996, it’s completely free, and its batch conversion feature handles JPG, PNG, WebP, TIFF, BMP, GIF, and dozens of other formats.
How to use IrfanView batch conversion
- Download and install IrfanView from irfanview.com (free, no bundled software if you uncheck during install)
- Open IrfanView and go to File → Batch Conversion/Rename
- Browse and select all the images you want to convert
- Under Output format, choose your target (e.g., JPG, PNG, WebP)
- Click Options to set compression quality, resize dimensions, or other settings
- Choose an output folder and click Start Batch
📸 SCREENSHOT NEEDED: IrfanView Batch Conversion window showing file list, output format dropdown, and Start Batch button
Tool 2: FastStone Photo Resizer — Best for Watermarking
FastStone Photo Resizer is specifically designed for batch image processing. It handles resize, rename, format conversion, colour adjustments, and watermarking — all in one pass. Free for personal use.
How to add a watermark to multiple images
- Download from faststone.org/FSResizerDetail.htm
- Add your images to the list on the left
- Tick Use Advanced Options and click Advanced Options
- Go to the Watermark tab
- Add text (your site name, copyright) or a logo image
- Set position, opacity, and font
- Click OK and then Convert
📸 SCREENSHOT NEEDED: FastStone Photo Resizer Advanced Options Watermark tab showing text watermark settings
Tool 3: XnConvert — Best for Complex Multi-Step Batches
XnConvert is the most powerful of the three. You can chain multiple actions in sequence: resize first, then sharpen, then add a watermark, then convert to WebP, then rename — all applied to a folder of images in one run. It’s free for personal and non-commercial use.
Download from xnview.com/en/xnconvert/. The interface is more complex than the other two, but the Actions tab makes the multi-step pipeline visual and easy to follow.
Compressing Images to Reduce File Size
All three tools handle compression, but for web use (reducing JPG/PNG size for a website), these online tools are faster for occasional use:
- Squoosh (squoosh.app) — browser-based, no upload limit, converts to WebP
- TinyPNG (tinypng.com) — excellent PNG and JPG compression, up to 20 images free per session
- Compressor.io — supports JPG, PNG, GIF, WebP, SVG
For offline bulk compression, IrfanView’s JPG quality slider (set to 80–85) reduces file sizes by 50–70% with no visible quality loss.
Fastest bulk resize:
IrfanView → File → Batch Conversion → Add files → Set output format + size → Start Batch
Warning: Always process copies, never your originals. Set IrfanView and FastStone to save to a different output folder — not back into the source folder.
Quick checklist:
- ✅ Downloaded IrfanView from irfanview.com (not a third-party site — avoid bundled installers)
- ✅ Set output to a separate folder before running the batch
- ✅ Used IrfanView JPG quality 80–85 for web images (good balance of size and quality)
- ✅ Tested with 5–10 images before running on the full batch
Frequently Asked Questions
Can I batch convert images to WebP on Windows for free?
Yes. IrfanView supports WebP output in its batch conversion. Install the IrfanView plugins package (available on the same page as the main download) to ensure all formats including WebP are available.
How do I batch rename images with a sequential number?
IrfanView’s batch tool handles renaming too. In the Batch Conversion window, switch to Batch Rename mode and set a pattern like photo_### — it will output photo_001, photo_002, etc.
Is there a way to batch edit RAW photos (Canon CR2, Nikon NEF) on Windows for free?
Yes — RawTherapee (free, open source) handles batch processing of RAW files. It’s more complex than IrfanView but covers professional-grade batch adjustments including colour correction, exposure, and noise reduction.
Conclusion
IrfanView covers 80% of batch image tasks. If you specifically need watermarking, FastStone Photo Resizer is worth the download. XnConvert is overkill for most people but invaluable if you run a complex multi-step workflow regularly.
For more Windows productivity tips, check out our Windows tips guide and the best free software for Windows.
Download IrfanView Free ↗ ↗More Free Windows Tools