Problems uploading photos onto Blogger

I'm having problems uploading photos onto Blogger, since it did a major
re-design of layout. It keeps downsizing all my photos to about 320 px
across.

Here's my 640px image (downsized by Blogger) .... which was probably
too wide to fit in this webpage space ...

Here's a 500 px version ....

Here's a 400 px version ....

I've had a look at the HTML code on this page, and all the widths are 320 pixels.

Blogger no longer accepts the HTML code from my Flickr site (unless I were to
translate it somehow into Blogger code). It will accept this photo uploaded onto
my Picasa web album, but Blogger downsizes it to 320 px width. I've also had
go at stretching the image out, by increasing the height and width measurements
in the HTML code, but the resolution of the photo is very poor.