The wiki seems to work fine, but embedded images aren't working.
Try to open one of the images directly (right click → select open image in new tab) to see if you get any errors.
If you get some PHP error or the message
The image can't be displayed because it contains errors one of your plugins might be broken.
If you don't see any error messages displayed, they might still appear in your error log. So, please check those. (If you don't have access to them, ask your provider.)
You may also want to use a download tool like curl or wget to download the image directly and compare your original image with the one you downloaded from DokuWiki. Whitespace and BOM errors can easily be detected this way.
If you get no content at all, make sure you haven't misconfigured the xsendfile option.
If thumbnails for small images work, but larger ones fail, you might hit a memory problem with libGD. Try configuring ImageMagick instead.