If you’re on a mobile device, it’s the blue icon with a white “F” on the home screen (iPhone or iPad) or in the app drawer (Android). On a computer, visit https://www.facebook.com and sign in with your username and password.

Use this method if you’ve already posted something on your own Facebook timeline and want to add a photo to the post.
 You can find it on your own timeline, where your posts are displayed in order (with the newest post at the top). To get there, tap or click your profile image at the top left corner of the page.,,, If you’re on a computer, it’s the icon that looks like a camera at the bottom left corner of the post.,

On a smartphone or tablet: Tap the photo you want to upload, then tap Done at the top right corner of the screen. To select more than one photo, just tap as many photos as you’d like.
On a computer: Click the photo you want to add, then click Open at the bottom right corner of the window. To select more than one photo press Ctrl (Windows) or ⌘ Command (Mac) as you click each photo.
 If you’re using a smartphone or tablet, it’s at the top right corner of the screen. The photo(s) will now appear in your original post.
Open Facebook.
Find the post you want to edit.Tap or click the arrow at the top right corner of the post.Select Edit Post.
Tap or click Photo/Video.
Select a photo.
Tap or click Post.
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