Using and handling images and their metadata
Thanks @Jonny Bradley and @Rick Sapir / Tiki for Smarties!
1. I don't want to use "image/*" as I might want to allow "application/pdf" as well. "image/jpeg,image/png" only shows relevant files in ubuntu, but file upload itself does not work at all. "image/jpeg|image/png" shows all files (including pdf), but file upload only works with *.jpeg, *.jpg and *.png files. So "|" works better than "," - contrary to what the docs stated - I udated them. Thanks for rubbing the "|" under my nose once again.
I did not find a setting in the options of the file gallery regarding file types other than "Podcast (Audio)" and "Podcast (Video)", so this does not help.
2. Removing the file upload button from the toolbar is a good beginning. I'll have to look into the other points on how to make my own button afterwards.
My use-case are users editing wiki pages. I don't want them to upload images without information on the creator and the license, as I have to make sure that my site is allowed to use them. So I need to remove file upload other than trough the tracker. So, when someone is editing a wiki page and wants to upload an image, I don't want them to break their workflow, copy the text so far into another window, cancel editing, navigate to another page to be able to upload an image, navigate back to the wiki page, go into edit mode again, copy back the work he did so far, and search through all the images in the gallery to find the one he just uploaded. I would not like to contribute in a wiki with such a bad workflow. Image upload must be possible while in editing mode on the wiki page.