In this era of wide screens and higher resolutions, I increased the maximum width for every future image upload (from 1920px to 2560px).
Yuck 
I’m not sure what I think to huge images on somewhere like here. Going from 1080 to 4K just means that server storage needs to be 4 times larger for the same number of images, and 1080p provides more than enough detail to work out what’s going on, or see the required detail on every image I’ve ever wanted to post online.
The size of screen and quality of camera that is required is significant for a 4K image to be fundamentally beneficial.
Hmm…
I did a test and the weight of images (4 MB+ images, but they are resized and compressed before being sent to the server), increased by about 55%. So, at the end we still are on a 500 to 800 KB scale for the final image size, that’s not so much regarding the disk space and even most of the Internet connexion of our fellow unicyclists, I guess… 
For the record, we currently have 27 GB of uploads (from which 95+% are from before Discourse I guess, but there was probably a low size limit, like 256 KB), and 95 GB free, on a disk of 160 GB. The server is scalable and the disk can be increased to 240 GB in a matter of minutes.
Sooo… Not really sure about this change. I’ll try to grab some other info. For example, I’d like to know how much users uploaded files (how many GB) since the migration to Discourse.
Images tests:
In terms of viewing comfort, it seems interesting only for very wide images (panoramic pictures) on a wide monitor with high resolutions. Kinda niche I think.
Also, a lot of people use the forum from their smartphone, where the change would be useless.
I reverted the change for now. Thanks for your insight. 
Discourse stores multiple versions of each image though right?
There’s the (compressed) original, the one as shown in the thread, and then the one shown when you click on it from the thread.
The compressed sizes are better than I thought, and I’d forgotten that Discourse does heavy compression in the first place, but I still don’t personally see the need for the images actually being that large.
I guess where it might make things better is the user experience of uploading, as resizing images is not always as straightforward as it should be on some operating systems (Windows I’m looking at you - Image Resizer Powertoy ftw).
What does the forum do at the moment on mobile (and on desktop) when you try and upload an image that’s too large?
Yes, it stores 2 images (as far as I know):
- The “thumbnail”, which is 960*500px max, very lightweight, and the “original”, which is often not the original, because…
- Discourse resizes and recompress large files, depending on a bunch of criteria.
Client-size resizing and compression (via a javascript library I believe) before sending to the server. It even allows to upload MASSIVE or ULTRA LARGE resolution images (but they’ll also be hugely resized and recompressed 
).
But still, in certain cases, Discourse won’t be able to sufficiently reduce the image weight, and it will be blocked by a “hard-coded” limit of 4 MB. Should be fairly rare though.
So the limit is 4MB after compression?
Yup.