CaesiumPH is a small, simple application that does one single job: compressing JPEGs images without any loss of quality. It means that the image is exactly the same as before the process, but about 15-20% smaller in size. So, you just save space without losing absolutely anything. I would try it out.
Although you probably didn't notice, Caesium applies a lossy compression. That means you lose some data during compression, but the software makes you think the opposite, by stripping data we don't clearly see with our eyes. CaesiumPH applies a lossless compression.
Yes, lossless. It means the image is the same, in every aspect. If you don't believe it and have some free time, check pixel by pixel. Or use a software, your choice.
Quite well, if you ask me. Ehm, I'm the developer. Anyway, it really depends on the image type. Since it works with JPEGs only (for now), the compression ratio is usually around 11-13% for photos taken with cameras. This numbers may grow up with special kinds of images, up to 20-25%. Let me remind you don't lose anything, uh.
No, compressed images are common JPEGs.
mozjpeg is the compression library used by CaesiumPH.
Yes, completely. Read the license here.