This website has a ton of very high resoluted images that have way more than 100 MB.
The files are licenced under CC-BY-4.0
Wesite licence note: https://www.eso.org/public/outreach/copyright/
Licence template on Commons: https://commons.wikimedia.org/wiki/Template:ESO
An example would be https://www.eso.org/public/images/eso1242a/
The biggest available file would be a *.psb file which is unfortunately a proprietary file format and can not be used.
The second highest resolution however is a *.tiff file with 3.9 GB