I'm just learning how to post bigger photos.....please bear with me...in the meantime enjoy an old photo of "The Max" making a mess of himself.
Here is how you do it....(Thank you to Megan!)First you must WIDEN your margins....
I use 880 for outer wrapper and 620 for main wrapper
This is how I am posting big photos....
I didn't want to use another photo hosting site because my mom and sister-in-law sometimes download photos from our site.
Go into your new post (or an old one, doesn't matter). Once you have uploaded your picture, click save draft.
Then go into the PREVIEW mode, where you can see the pictures with your text.
Click on a picture and choose "open link in new tab". It should open up in the new tab really really big.
Copy the image URL
Now.... go into the Edit HTML part of your post, out of "compose" mode. Find the SECOND picture link of your picture.
Now.... go into the Edit HTML part of your post, out of "compose" mode. Find the SECOND picture link of your picture. Like this, you want to replace ALL of the green, NOT the yellow:
http://1.bp.blogspot.com/_AGoLd370yHc/SsPQ6E1vD5I/AAAAAAAAEPU/xobkL_Q5Yh4/s1600-h/sundried+tomato+pasta.jpg">http://1.bp.blogspot.com/_AGoLd370yHc/SsPQ6E1vD5I/AAAAAAAAEPU/xobkL_Q5Yh4/s1600/sundried%2Btomato%2Bpasta.jpg" border="0" alt="" id="BLOGGER_PHOTO_ID_5387379275415359378" />
Replace the SECOND reference with what you just copied from your other tab as the new image URL.
Change the width to 600px for landscape photos (400px for portrait orientation) totally delete the height reference because it's irrelevant. You can preview it in Compose mode to see if it did what you wanted it to do.
This starts to become really fast and automatic. Kind of a hassle the first few times. In a long post, I'll often do a find and search to find the image addresses faster. You have to change each picture.