Imj is a web-based movie barcode generator, montage generator, and image analyzer/plotter for creating visualizations for your large image sets. You can learn more about it and see some examples in this blog entry, and if you make something cool, submit it to the Imj Tumblr archive.
It's been tested mostly in Chrome on a MacBook Pro, and it works pretty well for me. With other platforms or browsers, your mileage may vary. It uses your CPU to process these images, so lots of really big images may take up all your memory and/or a lot of time. Your computer may freeze up; it probably won't catch on fire.
Generally speaking, smaller resolution images produce just as a good of a barcode, montage, or plot, so if you have the choice, work with smaller images whenever you can. If you have problems getting this to work, please read some browser- and platform-specific notes.
Step 1. Load your images.
Select up to 9999 individual image files or a directory of files. Add more file select widgets if necessary.
Step 2: Choose your visualization style and set some options
Step 3: Review
Step 4: Watch it Happen
When the image is done loading, right-click and "Save As...", or use the download link above.