iPhoto instructions..

highlight your picture in the iPhoto 'Photo Library', (it should have a blue border when highlighted) then select 'Export" from the file drop down menu (or shift>apple key>E on keyboard) In the window which opens set the Format rocker from 'original' to 'jpg', click the radio button which says 'Scale images no larger than..' and set the width to 500 tick the 'Use extension' radio button and save to your desktop. Open blogger page>post>browse folder and upload as 'inline' hey Presto!