There's a problem with the configuration of your server.
When a image is requested directly (opening the URL directly on the browser) it displays correctly, but when it's embedded inside a page, it responses with a HTTP 302 redirect.
HEAD /images/thumb/a/a7/222830189_11653202548736095362.jpg/180px-222830189_11653202548736095362.jpg HTTP/1.1
Host: pokemon-go-wiki.ch
HTTP/1.1 200 OK
Cache-Control: public, max-age=604800
Expires: Sat, 30 Jul 2016 13:01:41 GMT
ETag: "31ea-57935b22-5349d6c553b5d0c2"
Last-Modified: Sat, 23 Jul 2016 11:55:14 GMT
Content-Type: image/jpeg
Content-Length: 12778
Date: Sat, 23 Jul 2016 13:01:41 GMT
Accept-Ranges: bytes
Connection: Keep-Alive
HEAD /images/thumb/a/a7/222830189_11653202548736095362.jpg/180px-222830189_11653202548736095362.jpg HTTP/1.1
Host: pokemon-go-wiki.ch
Referer: http://pokemon-go-wiki.ch/index.php/Spezial:Dateien
HTTP/1.1 302 Found
Date: Sat, 23 Jul 2016 13:02:36 GMT
Accept-Ranges: bytes
Cache-Control: no-cache, no-store, must-revalidate, max-age=0
Location: http://
Connection: Keep-Alive
Maybe your server has a rule "trying" to prevent image hotlinking, but it's broken