Unfortunately the pixelization is due to the compression. I am not sure if I did the correct thing just attaching it. The original is pretty sharp and I can keep zooming in for quite some time and it stays sharp..
How did you convert your pictures?
I am doing all of my PP in Aperture and then uploading to my website which runs Gallery software. For uploading I use Gallery Remote so I get full sized images available on my website and it does a nice job with the web compression for pasting URLs. When I post a photo to a forum I use the URL from smaller "mid-sized image" that Gallery compressed.
If you have an interest in using Gallery software it is free and offered here: http://gallery.menalto.com/ and if you don't already have a web host there are some that are certified to work with Gallery here: http://gallery.menalto.com/wiki/Web_Hosting_Referral_Page
I am still running a very old version of Gallery 1.5 but it works well for me so I haven't messed with it yet. If you want to see my Gallery for an example... This would be a thumbnail page:
http://www.sealec.com/faulk/album185?page=40
This would be a mid sized photo: http://www.sealec.com/faulk/album185/IMG_0504 this would be that mid sized photo's URL that I would post to a website: http://www.sealec.com/faulk/albums/album18..._0504.sized.jpg
And this would be the full sized photo: http://www.sealec.com/faulk/album185/IMG_0504?full=1
You can click on any photo to see how it goes on my site. Click once on a thumbnail for mid sized, click again for full sized.
Sorry to be so long winded, I am just trying to be (probably overly) helpful.