A few days ago I needed an image magick command that scales and crops a picture on its center. I looked up the last project I used it and found the magical line (pun intended). I'll post it here as a future reference for my self and perhaps it will help others as well.
convert myPhoto.jpg -resize 200x200^ -gravity Center -crop 200x200+0+0 +repage myThumb.png
The "myPhoto.jpg" picture is being scaled down to 200 pixels - width or height (the one that has lowest size), then it's cropped on the center. "myThumb.png" is the name of the photo that's being created.