a) Check what the HTML tag shows for this figure
When i inspect the image element, the tooltip says image.media | 412x704 (which is the actual size of the image).
The html tag for it is
<img src="/gdds/sa/lib/exe/fetch.php?media=test.png" class="media" alt="">
b) What template is this. try the vanilla Dokuwiki template with nothing else on the page other than the figure
It's adoradark. i switched back to the default dokuwiki template, but the problem persists.
What happens if you right click on image and say "view image" (or whatever your browser says).
If i right-click and select Copy Image and paste it into Photoshop, it's at the proper 412x704px.
In Chrome, when i right-click and select "Open image in new tab," the image (embedded in a DokuWiki page with the address myurl/lib/exe/detail.php?id=myPageName&media=test.png ) displays at 613 pixels wide. If i right-click the image and select Copy Image Address, and then paste the address into the URL field in a new tab, the image displays at 482px wide. Chrome's Zoom Level is at 100% in each case.
In Internet Explorer, the image displays at the proper 412px wide on the DokuWiki page (although IE defaults to a 150% zoom level - i had to crank it down). When i right-click and select "Open link in new tab" and it takes me to the image embedded in a DokuWiki media page, the image width is 409px at 100% zoom.
If i Save Image/Picture As... from either Chrome or IE and open the saved image in Photoshop, the image is the proper 412x704.