See this site for info - the following is an extract from their FAQs page. There is more info located at: http://www.jpegmini.com/main/faq
Why should I use JPEGmini?
With JPEGmini you can store more
photos on your hard drive and online photo service accounts, attach more
photos to your emails, and upload your photos faster to the web. If you
have an image-intensive website, your pages will load faster, improving
user experience, monetization and SEO, and you’ll also reduce your
storage and bandwidth costs.
Is JPEGmini a new file format?
No.
JPEGmini files are in standard JPEG format, which can be viewed and
edited by any browser, photo software or consumer device.
How is JPEGmini different from JPEG?
JPEGmini
files are optimized JPEG files, whose parameters have been tuned to
significantly reduce the file size without affecting perceptual quality.
How do I make sure that the quality of my photos is not affected by JPEGmini?
JPEGmini
technology has undergone extensive user testing according to the ITU
BT.500 standard, which proved that average users could not distinguish
between original photos and JPEGmini photos. You are welcome to test the
quality on your own photos: After optimizing them with JPEGmini,
compare them side by side at 100% zoom (“Actual Size”), where each pixel
on the screen corresponds to a pixel in the photo.
Can I print my photos after JPEGmini optimization?
Absolutely.
Since JPEGmini does not alter the perceptual quality of your photos,
you can print them at the same size you would print your original
photos, and the prints will look exactly the same. Watch JPEGmini Pro
Being tested under the loupe https://youtu.be/xdndN5kobdg
Can I use JPEGmini after using other image editors or compression software?
Yes,
JPEGmini accepts standard JPEG files as input, and outputs standard
JPEG files as well. So any image editor, effects software, photo
management software, etc. can be used before or after JPEGmini
optimization. We recommend using JPEGmini as the last step in your photo
processing flow, since any JPEG encoding (due to additional edits or
processing) applied after JPEGmini optimization will eliminate the
optimization benefits achieved by JPEGmini.
Does JPEGmini affect the metadata of my photos, such as the EXIF data?
All
the EXIF metadata of the original photo is retained in the JPEGmini
version. Users of the JPEGmini Server have an option to remove metadata
if they want to further reduce the output file size.
What is the typical file size reduction I can expect from JPEGmini?
This
depends on the resolution and quality of the original photo. For
high-quality, full resolution photos produced by digital cameras, you
can expect a reduction of 50%-80% in file size, while web images are
typically reduced by 20-40%.
I tried JPEGmini and the file size reduction was very small. What happened?
JPEGmini
achieves the highest file size reduction for first-generation photos
created by digital cameras. Using photos that have been edited, re-sized
or processed by photo editing software may cause lower reduction
ratios.
What is the JPEGmini Web Service?
The JPEGmini Web Service is
a free online service for optimizing your photos using JPEGmini
technology. You upload your photos to our server, and then download the
optimized JPEGmini photos back to your computer.
Do I need to register in order to use the service?
You can optimize single photos without registering to our service
here. If you want to upload a collection of photos, you should register for the service
here.
How much does it cost to use the JPEGmini Web Service?
Using the JPEGmini Web Service is free both for single photos and for unlimited album processing.
Is there a limit on the number of photos I can upload to the JPEGmini Web Service?
Each
album that you upload can contain up to 1000 photos, and can be up to
200 MB in size. You can upload as many albums as you want.
