Imagemagick

convert	convert between image formats as well as resize an image, blur, crop, despeckle, dither, draw on, flip, join, re-sample, and much more.
identify	describes the format and characteristics of one or more image files.

Option	Wirkung
-alpha remove	entfernt Transparenz
-background white	setzt weißen Hintergrund
-trim	schneidet den Rand des Bildes weg

# general JPG to PDF
convert img1 img2 img3 ... out.pdf

# multiple JPGs to one PDF
convert -append img1 img2 img3 ... out.pdf

# convert page 17 in 300dpi
convert -density 300 input.pdf[16] output.jpg

find -name "*.jpg" -exec mogrify -resize 75% -quality 80 {} \;

find -name "*.jpg" -exec mogrify -strip {} \;

Tools