Here I used glob style input. I also had to pad because the image height was odd
ffmpeg -framerate 10 -pattern_type glob -i '*.jpg' -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" out.gif
ffmpeg -framerate 20 -pattern_type glob -i '*.jpg' -vf "scale=trunc(iw/4)*2:trunc(ih/4)*2" out.gif