Mishka OP is one of those humans who seems to spend their life helping other Bloggers getting things fixed. I posted the following today at Blogger help:
Turns out that Blogger modifies the pictures when they are uploaded soHe has helped some to get headers up to this size, but I have used a much larger one and seem to be lost.
even if you try to upload a 900px picture to cover the entire banner
area on a stretch or lefty template, it won't do it anymore....the
biggest you can get is a 740 with new uploads (apparently this changed
a couple of months ago). Those that uploaded larger pictures a while
back and have stayed with them are able to get some of them to stay
Another person has stated that there will be no return to the former situation in Blogger, but that there might be options for sizing of pictures in the header - within limits.
Does anyone know of other good hosts for blogging?