Manipulate and Convert Images
apt-get install imagemagick

convert SOURCE.jpg DEST.png # Convert a JPEG image into PNG 
convert -resize 50% SOURCE.jpg DEST.jpg # resize SOURCE.jpg at 50% of the original size, and save it as DEST.jpg
convert -resize 600x300 SOURCE.jpg DEST.jpg # resize SOURCE.jpg to 600x300 (width x height) pixels, and save it as DEST.jpg
convert -resize 600 SOURCE.jpg DEST.jpg # resize SOURCE.jpg to a width of 600 pixels and relative height, and save it as DEST.jpg
convert -resize x300 SOURCE.jpg DEST.jpg # resize SOURCE.jpg to a height of 300 pixels and relative width, and save it as DEST.jpg
convert -thumbnail 150 SOURCE.jpg DEST.jpg # create a thumbnail of SOURCE.jpg with a width of 150 pixels and relative height, and save it as DEST.jpg # the difference between -resize and -thumbnail is that -thumbnail strips all meta data (like EXIF information) from the original image
convert -size 1x1 xc:none IMAGE.png # create a transparent .png image sized 1 x 1 pixels
convert -thumbnail x100 PATH/FILE.pdf[0] THUMBNAIL.png # create a thumbnail with a height of 100 pixels for the first page of a PDF document
convert -thumbnail x100 PATH/FILE.pdf THUMBNAIL.png # create a thumbnail with a height of 100 pixels for every page of a PDF document

EXIF Information
apt-get install exiftool

exiftool FILE.jpg # show EXIF tags inside a JPEG image
exiftool -geotag= FILE.jpg # remove geographical coordinates from the given image
exiftool -all= FILE.jpg # remove all EXIF information from the given image
for i in PATH/*.jpg; do echo "Processing: $i"; exiftool -all= "$i"; done # remove all EXIF information from all the JPEG images in the given PATH

apt-get install exif

exif FILE.jpg # show EXIF tags inside a JPEG image
exif -im FILE.jpg # return EXIF tags inside a JPEG image in a machine readable format (-i ID instead of tags, -m tabs delimited output)
exif --ifd=0 -t TAG --set-value=VALUE SOURCE.jpg -o=DEST.jpg # set TAG as VALUE in SOURCE.jpg and save the resulting manipulated image as DEST.jpg
exif --remove --ifd=0 SOURCE.jpg -o=DEST.jpg # remove all EXIF information from SOURCE.jpg and save the resulting cleaned image as DEST.jpg
exif -r SOURCE.jpg -o=DEST.jpg # remove the thumbnail from SOURCE.jpg and save the resulting cleaned image as DEST.jpg
exif -e SOURCE.jpg -o=THUMBNAIL.jpg # extract the thumbnail from SOURCE.jpg and save it as THUMBNAIL.jpg 
exif FILE.jpg -n=THUMBNAIL.jpg # add THUMBNAIL.jpg to FILE.jpg and save the resulting manipulated image as FILE.jpg.modified.jpeg