On my local i cannot see the users thumbs picture and if i post image, they don’t get lightboxed.
I thought was a problem with sidekiq but i run bundle exec sidekiq -q critical,low,default -d -l log/sidekiq.log and still don’t see images.
I follow this guide to install discourse and i have succesfully install and add imagemagick, helvetica font and all the other image related stuff.
Any suggestion on what I can try to make it work?
If the post was created before sidekiq was running, maybe a post rebake will do it.
Unfortunately it doesn’t 
i also did the same on my other computer (still a mac but more recent) and i’m also not able to see lightbox there.
What can i try more?
Have you tried similar weight, similar dimension images of different mime type?
i.e. jpg, png etc.
I just tested locally, running latest and running sidekiq with bundle exec sidekiq -d -l log/sidekiq.log and large images (3k x 2k) are working fine.
Look like that bundle exec sidekiq -q critical,low,default -d -l log/sidekiq.log is different from bundle exec sidekiq -d -l log/sidekiq.log
because i can now see them in lightbox (i had to recreate the post of course)
thanks @Falco!