Determine compression level of JPEG image online
Select a .jpg picture on your computer or phone and then click OK. After that, will provided information about the level of quality, with which has been compressed jpeg file. All standard jpg pictures has level of quality from 0 to 100. Compession or quality level of jpg from 90 to 100 means, that JPG picture was saved with the highest possible quality and low compression level. On this site, you can still get detailed EXIF information and to determine that it is a progressive jpeg picture or not.
For example, large pictures on website Vkontakte are saved with the quality 87, previews in the Google search for pictures - with quality of jpg 74.
The original image is not changed. You will get only quality (compression) level of JPEG from 0 to 100.