Because WP usually flags (and removes) iFrame HTML tags, you're better off using CSS or a plugin (assuming you're using WordPress). It's usually easier to manage the page you're calling. If you have access (and write permission) for the page your calling, it's known to be a better practice to edit that page instead of the constantly changing the front-end and wrestling with WP. You'll also have issues if you don't have an SSL certificate and you're calling a site that does, each site has to have the same Hypertext Transfer Protocol.
Little Web Hut has a decent HTML tag tutorial. It's out of date a bit, but it will work. But, again, I would look to use CSS for this, or if you need a more dynamic answer give some photo plugins a try (if you're using WordPress).
I've used
this WP iFrame plugin with some good results, in my case I was aggregating Amazon product listings from a specific account into an independently hosted site and therefore had no write access for the page I was calling.
There's a really, really good article on Kinsta about this very topic. I don't really like Kinsta, they tend to revolve their articles around sponsors, but
this article is well written and fairly current.
Lastly,
here's a CSS "trick" that will likely work, but CSS "tricks" don't tend to have a long shelf life generally speaking.