Need to compare two photos side-by-side? Using the convert tool, you can quickly stitch two or more photos together and compare the result in any image viewer:
convert photo1.jpg photo2.jpg +append compare.jpg
The example command above stitches photo1.jpg and photo2.jpg from left to right (i.e. photo1.jpg + photo2.jpg), but you can use -append instead of +append to reverse the order (i.e. photo2.jpg + photo1.jpg). In both cases, the stitched image is saved under the compare.jpg name.
If you use KDE as your preferred graphical desktop environment, you can create a context action to stitch file pairs in the Dolphin file manager. Create a text file and paste the following code into it:
[Desktop Entry] Type=Service ServiceTypes=KonqPopupMenu/Plugin MimeType=image/JPG;image/JPEG;image/jpeg;image/JPG;image/jpg; Actions=Compare [Desktop Action Compare] Name=Compare Photos Exec=convert %F +append compare.jpg Icon=image-x-applix-graphics
Save the file under the compare.desktop name and move it to /usr/share/kservices5/ServiceMenus:
sudo cp compare.desktop /usr/share/kservices5/ServiceMenus/
Open Dolphin, select a pair of JPEG files you want to compare, right-click on the selection, and choose the Actions → Compare Photos action to resize the image. This generates a compare.jpg file with the selected photos side by side. You can then use your preferred image viewer to examine the photos.
This is an excerpt from the Linux Photography book. Get your copy here.
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Scribbles and Snaps 
Dmitri,
Hello.
Thank you this is a superb Linux-ista tool!
matthew
This is a great tip. Very hand for KDE users like myself.