How can I overlay an image (a transparent PNG file) over all the “background” images in a directory using command line?

Question

I have a transparent PNG file (a picture of a cow)

I have a folder that contains images of grass, mountains, rivers and so on.

I want to overlay the cow image onto those background images only by using Linux command line.

Answer 1

convert tool from the ImageMagick package

You can merge images using ImageMagick Layering

I.e.:

convert -page +0+0 grass.jpg \
    -page +256+0 clouds.jpg \
    -page +512+0 cow1.png \
    -background none -layers merge +repage merged.jpg

Batch convert several images

Let's suppose that you have two images: 1. grass.jpg as first image 2. and cow1.jpg, cow2.jpg etc as second image to merge

So, your bash script is:

for image in cow*.jpg; do
  convert -page +0+0 grass.jpg \
    -page +100+100 $image \
    -background none -layers merge +repage $image-merged.jpg
done