ok so for big photos in blog spot i will just copy an email i got here explaining it i hope this is ok and allowed..

this is all in the html tabbefore publishing this also must be done to evey picture on every post its not a one time thing...

Kay so when you upload an image on to blogger it looks like this:

<a href="http://1.bp.blogspot.com/_jh_B-b1o1zg/SWhJSiiop1I/AAAAAAAAA-Q/-39hH57eApI/s1600-h/Day+71.jpg"><img style="display:block; margin:0px auto 10px; text-align:center;cursorointer; cursor:hand;width: 400px; height: 286px;" src="http://1.bp.blogspot.com/_jh_B-b1o1zg/SWhJSiiop1I/AAAAAAAAA-Q/-39hH57eApI/s400/Day+71.jpg" border="0" alt=""id="BLOGGER_PHOTO_ID_5289558345205196626" /></a>

what you are going to do is delete this part...width: 400px; height: 286px; (in bold above) make sure you leave in the parenthesis but delete the semi colon.

so it will look like this....

<a href="http://1.bp.blogspot.com/_jh_B-b1o1zg/SWhJSiiop1I/AAAAAAAAA-Q/-39hH57eApI/s1600-h/Day+71.jpg"><img style="display:block; margin:0px auto 10px; text-align:center;cursorointer; cursor:hand;" src="http://1.bp.blogspot.com/_jh_B-b1o1zg/SWhJSiiop1I/AAAAAAAAA-Q/-39hH57eApI/s800/Day+71.jpg" border="0" alt=""id="BLOGGER_PHOTO_ID_5289558345205196626" /></a>

Then you are going to change the s400 to s800, (in bold above).

thats it !!