Hi,
Try hosting images externally, like on Flickr or a similar service. See if the speed improves.
If yes > load the same image in a post and also outside WordPress, under a normal folder and see if both load at the same speed.
If no > We need to dig deeper into WordPress to see what the issue is!
Thank´s for the advice. Tried including a pic that I hosted on flickr in a post and it loaded lightning fast. So it must be some issue with my hosting service, right?
Well, can confirm that only after hosting the image outside WordPress. Have you tried that and compared the speed?
Yes:
Same image from different sources in a wp-post:
Speed outside wp (flickr) TTFB: 415 ms
Speed inside wp TTFB: 2570 ms
This bothers most regarding the header image. Is there any way to hard code the header so that it is loaded from my flickr account?
Yes, you will need to edit the theme files.
You might also need some CSS editing as well.
Ok, found it. I changed the css code in custom-header.php and added the url to the flickr-image. It seems do have done the trick :).
Thank´s for your assistance, dinsan!
Glad to know that you have at least a temporary solution!
Dinsan