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I have 50,000 high resolution JPEG photos, where a couple of them might occasionally be needed, about once a year.

I wanted to zip them to save disk space, except that zipping gives no space benefit - so trying to reduce the images disk usage using winzip, winrar or 7zip was not successful.

Is there any software or algorithm similar to zip to compress image size on hard disk for storage without loosing any image information?

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What format are the photos in now? –  William Jackson Sep 6 '12 at 18:14
@WilliamJackson mainly jpeg –  Timo Huovinen Sep 6 '12 at 18:15
Yes, jpeg is already a compressed format. The only way to make the file size smaller is to sacrifice image quality. –  William Jackson Sep 6 '12 at 18:17
@TimoHuovinen I think that JPEG optimizers is what you want to look for; The goal is to reduce the size of photographs without affecting their perceptual (noticeable) quality. I use JPEGmini, though I don't use it for more than few dozens photos a month. –  amiregelz Sep 6 '12 at 18:18
@amiregelz can't find anything about jpg optimizers in google, what exactly do they do? –  Timo Huovinen Sep 6 '12 at 18:20
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3 Answers

up vote 3 down vote accepted

From Wikipedia:

Image compression may be lossy or lossless. Lossy methods are especially suitable for natural images such as photographs (e.g JPEG files) in applications where minor (sometimes imperceptible) loss of fidelity is acceptable to achieve a substantial reduction in bit rate.

JPEG optimizing is considered to be a very efficient method to reduce JPEG file size while preserving the image quality. The goal is to reduce the size of photos without affecting their perceptual (noticeable) quality. The optimized image should look identical to the original image to humans, even if it was reduced to 30% of its original size or even less.

There are several tools for JPEG optimization, mostly command-line tools (libraries); the most popular ones are jpegtran & jpegoptim (Google PageSpeed recommends using them too).

If you're looking for a more user-friendly tool, I recommend using JPEGmini. It's an online service, and it's free for personal use. I don't know if it's the best tool to use in order to optimize thousands of photos (see FAQ), but from my experience, it's doing a great job optimizing JPEG photos.

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edited as you are using jpg's: this answer suggests reducing the quality of your jpg's just a little bit to save space.

JPG files are already optimised so compression will not help you.

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Using a tool like 7-zip can create an archive that's a few percent smaller. Not great, but it is something. For an archive of a few hundred photos that I had, I saved about 4% with 7-zip.

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