It's all about optimization
It's all about optimization
It is not well known that JPG images can be partially compressed - you can compress and blur the background while leaving the the foreground crisp and clear. In situations where your background is a dull or dark negative space, you can squeeze out a few extra bytes with this technique. Especially effective when the background is a solid color.
original JPEG image - 27152 bytes.
uniform compression - 4983 bytes. Both foreground and background are equally compressed.
selective compression - 4109 bytes. Note how the ladybug is still crisp, while the background shows typical JPG compression artifacts.
The above images were optimized using Advanced JPEG Compressor