When you post something, there are icons above where you type. Near the filmstrip icon (for video posts), there are two icons that look like a polaroid with a tree, one has like a floppy disk also. If you move your mouse arrow on the icons, they will say: "Host an image" or "Image". If you have a url or web address for the photo, use the "Image" and just copy/paste the photo url.
If you want to upload a photo, use the "Host an image" icon. Hit the browse button to find the photo on your hard drive and click upload. Three website urls will appear: one for a thumbnail image, second for the full size image (use this) and the third makes a url on the post. You only need to use the second one. Copy and paste the second (middle) web address and just paste it into where you type. And send the post.