For those who have not tried this here are some simple steps and tips, it is as easy as posting a picture on Facebook.
1) Click in the insert image icon above 
2) Select the camera icon at the end of the source category.
3) Choose file location from your device or PC.
- On my android phone the source was located in >Documents>Gallery. Your device may differ slightly.
4) Choose image and voila, the picture should appear in your post.
I hope this helps, happy posting !