I use picsart and a stamp template, super duper easy!! just upload the template to the app and mold the image to fit nicely under the border, then move the image layer down to fit under the stamp
https://www.tumblr.com/puppizai/771198264475320320/%F0%93%8F%B4-stamp-templates
(You can find a bunch on tumblr, just credit when needed ofc)
I believe you can use any editing app that allows you to stretch the images, picarts is just my preferred. alsoo you may have to edit the image to be smaller so I use ezgif for that, then upload the stamp using post image
https://ezgif.com/resize
https://postimages.org/