Image quality

What quality is the right one?

Often images can be compressed more for viewing on a full HD Screen (TV or PC), resulting in a smaller file without differences for the human eye.

Quality is too high

Viewers can't see any difference in the quality.
Files take up much space, copying and loading is slower. 

Quality 100% File size: 1'200 KB	Quality 90% File size: 410 KB	Quality 80% File size: 270 KB

Quality vs. size is right

Details begin to be lost. However, on most pictures, viewers probably won't see any difference in the quality.

Quality 70% File size: 220 KB	Quality 60% File size: 180 KB	Quality 50% File size: 160 KB

Quality is too low

Images getting fuzzy.

Quality 40% File size: 140 KB	Quality 30% File size: 120 KB	Quality 20% File size: 90 KB

Conclusion

For viewing on a HD screen, a quality around 60% will bring the smallest file without any noticeable lost of quality.