* Maximum size per picture: 1.5 Mb
* Maximum dimensions: 1920 x 1600 (pixels)
Click on 'upload attachment' :
* Click on 'Browse'
* Look for the picture you want to upload
* Click on 'Add the file'
Select the place in the post where you want the picture to appear and click on 'Place inline":
Big pictures (bigger than 1024 x 768 (and smaller than 1920 x 1600 maximum) are automatically resized for display. If you want to resize your picture and save some disk size look here: How to resize