[biryani_chicken]

Here is how you can do it with ImageMagick:

`convert -gravity center -background black -compose Copy -resize 800x450 -extent 800x450 input.png output.png`

Sadly I don't know how to do it without specifying the size in pixels. Using `16:9` for resize and extent doesn't do the trick.

[bigiain]

Do you have instructions so your mom could do that? Or would you just send here to the OPs website?

I know which I'd do...

[TacticalCoder]

You're bringing in the moms... Does yours read HN?

A certain audience does enjoy technical hints and explanations. Heck, ImageMagick / convert are part of quite some workflows on servers...

[bigiain]

Fair point... :-)

[fock]

yes. Figuring out the size thing is a technical problem. Then you can put the resulting script into a desktop-iconifiable format where she can just drag-and-drop her image onto. No website needed and just as simple as the website.

[ducktective]

One can utilize `zenity` with that command to fire up a GUI filepicker and input box for sizes.