I had a closer
look at the generated HTML and found that both wiki links create the same HTML:
<img
src="../wiki_uploads/5/51/My_picture.png" />
That relative path is wrong for a subpage as
there's one path level missing. So I suppose the problem has something to do with my
path settings.
I found the solution. I had to change the upload path so it includes the article path
like so:
$wgUploadPath = "{$wgArticlePath}/../wiki_uploads";
Thanks again for your help
Frank
Usually, it is set based on wgScriptPath:
$wgUploadPath = "{$wgScriptPath}/wiki_uploads";