Ha lenne időm megírnám neked a scriptet, de nincs :(
Erre indulj el:
xloadimage -identify kep.jpg
Szerk: a megoldás:
convert mit.jpg -resize 100x100 hova.jpg
By default, the width and height are maximum values. That is, the image is expanded or contracted to fit the width and height value while maintaining the aspect ratio of the image. link