I had acquired some high quality images and was willing to encode them into a video, but ffmpeg default settings was always outputting a ugly video which had 1280x720, but with lots of artifacts.
After googling a little, I've found:
Digging a little more on the comments I've found:
So, the key was the -vb flag!
ffmpeg -i Image-%d.jpg -s 1280x720 -aspect 16:9 -r 24 -vb 20M teste.mp4