Question about automating cropping process

I trie this code: montage *.jpg -tile 2x -background white -geometry +2+2 result.jpg

It results in one big file that has all the images in it- and there’s a gap between pairs

If I try with one pair of photos only, the gap is still there between the 2 photos and the new file size is much smaller than the original file. Original files are 450kB each but resulting file is 198kB

Don’t know what to do now - and I have 800 pairs of photo to join

I’m going to post this afresh as it’s own question