@Billy Batson Yes you can. To edit an image that you have already uploaded you need to find it in the inage selection panel first. When you hover your mouse cursor over the image you should see two links appear below the image: edit and preview.
@pikahyper: It's actually stored in "localStorage." Deleting the value depends on what browser you're using. In FireFox you can delete it by deleting your cookies using the "Everything" time range. In Chrome you can delete it by using the "Delete cookies and other site and plug-in data" option in the "Clear Browser Data" panel.
edit: Images that aren't in the viewport (below the bottom edge of the window) when the load is triggered will fade in. I've also increased the trigger distance to 500px below the edge. These changes will appear after the next deploy.
@pikahyper: I added some code to defer the loading of some images around the site. In theory they should load if they're in your viewport or you scroll to within 200px of the image. All avatars should behave this way as well as the images in the footer (cross-site promotions) and the thumbnails for news and videos. Not all images are deferred but I'll be adding more to the list this week.