HOWTO batch resize pictures
Resize and apply prefix:
$ for file in *.jpg; do convert $file -resize 25% re_$file; done
Add suffix _re, place the files in parent folder
$ convert *.jpg -resize 80% -set filename:f '%t' ../'%[filename:f]_re.jpg'
Will place converted files in the folder above.
The option -set filename:f ‘%t’ sets the property filename:f to the current filename without the extension. Properties beginning with filename: are a special case that can be referenced in the output filename. Here we set it to ../’%[filename:f].jpg, which ends up being the image filename with the extension replaced with _re.jpg in the parent directory.