What is the default JPG image quality for derived images?

When the JPG image quality isn't specified, the default quality being used is 90 (90%). If the original JPEG quality is less than 90% and no quality is specified, we don't change the JPEG quality.

You can manually set the quality parameter (q in URLs) to the value your require (1-100).

For example, the following sets the JPG quality of the image to 70% of the original image's quality: 
http://res.cloudinary.com/demo/image/upload/q_70/sample.jpg

For more information:
http://cloudinary.com/documentation/image_transformations#adjusting_compression_quality