ImgeMagick

Reference : http://www.imagemagick.org/Usage/annotating/#anno_below

How to create thumbnails :
mogrify -resize 80x80 -background white -gravity center -extent 80x80 -format jpg -quality 75 -path thumbs *.jpg

Adding label to bottom of picture
convert 133-20150823152553-00.jpg -background Khaki label:'Faerie Dragon' -gravity Center -append anno_label.jpg