@shammyshiggs is right!

BUT
Sometimes the site Doesn't reconise the photo so you have to use markdown:
! [] ( )
Note: the are NO spaces between them.
For a better understanting I made a tutorial with clear example :
https://steemit.com/steemit/@cynetyc/how-to-upload-images-an-videos-on-steemit
And check olso on how to center in your post the image and videos :
https://steemit.com/steemit/@cynetyc/how-to-center-images-and-videos-on-steemit