One of the most unknown features of WordPress is that it automatically compress any JPEG or JPG images that you upload via the Media manager or edit within the blog post image editing tool along with the thumbnails of the image in question. Not only does this confuse and frustrate webmasters and web designers but it continually degrades the quality of your photos and graphics over time, meaning that data loss grows and visual quality is evermore hurt.
Instead of an arbitrary “automatic” compression of images e.g. 90% that WordPress implements, it makes much more sense to crop images to an appropriate size (dimensions) and then pre-compress before uploading them. This is easily (and efficiently) done in popular editing programs like Photoshop >> Save For Web or online with free tools like www.jpegmini.com and can be done only to the extent that the designer chooses, to ensure quality and visuals remain intact.
For this reason we are releasing a new free plugin Disable Image Compression.
We will soon be installing this as a Must Use Plugin for all our managed hosted clients. Cheers!