Appending images vertically in ImageMagick

For vertical stacking (top to bottom):

convert -append 1.jpg 2.jpg out.jpg

For horizontal stacking (left to right):

convert +append 1.jpg 2.jpg out.jpg

Use -append to stack images top-to-bottom.

Use +append to stack images left-to-right.

Source: http://imagemagick.org/script/command-line-options.php#append

For latest imagemagick from V7 , the following is command

magick input1.jpg input2.jpg -append out.jpg