This didn’t work for me: I did go to ‘Add an image’, ‘From my device’, clicked on ‘Upload’ and then it showed me the snipped with .jpg as file extension.
I just did it again and it was the same. Then again and now it’s .png, then again: .jpg, then .png…
There may be some caching issue or maybe there are multiple image conversion workers which behave differently.
e.g. I’ve now uploaded twice the file ‘cemetery resized (v3).png’ and got this as result:
![Thimbleweed Park™ Forums fixes - cemetery resized|690x50](upload://w0TD6KiJEWvR3KC8PgMrNDshokX.jpg)
![cemetery resized (v3) (1)|690x50](upload://tPT7xZNVM008vvkBst05ZZEoSZp.png)
Note the different filenames which actually don’t match the filename I’ve used at this point in time, but were older ones I’ve used previously (files which had the same content).
It would be smaller when using a simpler algorithm (like nearest-neighbour) but for down-scaling that’s not what I want to do. Size issues were a concern for userstyles.org only anyway which I didn’t want to use anyway.
It doesn’t really matter in this case because after uploading to Discourse similar optimisation is applied which results in the file I am referencing in the style.