Selfhosted

I've searched around and can't find this but it seems like someone must have created this already. I am hoping to find a self-hosted image resizer app. I frequently need to take photos from my phone (etc...) and make them small enough to post online.

For instance, my lemmy instance (lemm.ee) only allows images in posts if they are smaller than 500KB but my phone's photos are always larger than that.

In a perfect world, I could just browse to a local server app, upload an image, select a size to resize it to, hit Go and then download the smaller image. It doesn't have to allow any other editing and it shouldn't store images long-term. I want to self-host so I don't have to upload my images to random web sites I know nothing about.

I would be happy with a FOSS desktop app I can install in linux too, but then I couldn't access it from my phone. The Android apps I found for this either look scammy or include tons of ads.

Anyone know of such a thing? Thanks!

EDIT - UPDATE:

Thank you for the great suggestions. I've installed Image Toolbox on my Android phone and that looks great. It both has a ton of tools but also makes this resizing task very straightforward. Not sure how I never found that before.

But for my desktop, I started writing a PHP app to run in my existing nginx web server. It runs the suggested ffmpeg command under the hood, and since I am the only user on this server, this works very well for me.

That's working now so I am going to tweak a few things and then use it for a while. (Before anyone asks, I started based on the Python recs here, but couldn't get it working (PIP couldn't add Flask because PIP couldn't find PIP???) and so switched to PHP since my local server was already using that from another home-made app. This (PHP) was not as hard as I was afraid it would be, with help from Duck Duck Go's AI chat bot.

I used my php app to shrink this file!

Thank y'all - this is resolved now.