I too am on the mobile website and.it's pretty simple! I'm young though and.used to this :p I'll take screen shots and demonstrate.
First, there should be an icon that looks like a photograph. Like so.
Click it and you should get this.
Hit upload from my device (unless of course you have a link)
Next you should get this. Hit documents (or.something similar, I'm on Android) because camera is taking a new photo)
You should get something like this where you can choose your photo.
Choose one and you.will get this.
Simply hit submit and voila!
I'm not that old Mine works exactly like that... except the last step. When I hit submit, it fails to add the image to the box. Everything else appears to work, but it just doesn't embed the image. Funny thing is, it worked a few times, but won't anymore. I even try it on occasion to check it.