Was this photo taken by a cell phone camera and do we know who took the picture?
The quality of this picture is very bad, like a cell phone pic, what I find odd is why would someone take a picture and keep it of Caylee from behind that really looks odd.
I have been thinking hard about this pic and here's my take: my home has many sliding glass doors that look out onto our pool/patio cage and they are taller than the ones shown here so I feel that it's possible that Caylee would have been tall enough to reach the handle at her age and height.
Sliding glass doors are not hard to open for children but I think that young children find it easier to push and pull doors open instead of slide doors open, in this picture it looks likes the the door was already cracked open and Caylee is trying balance herself while putting her head through that crack and call out to someone, it does not look like she is trying to open it to me. Sliders have screws at the bottom that can be adjusted to make them glide easier, I have heard of parents adjusting the screw at the bottom to make the doors heavy and hard to pull to prevent kids from opening them, so I find it hard to believe that CA & GA did not take any precautions to avoid an accidental drowning, these are experienced parents and know that the house had to be baby proofed.
In my house before my son was born I paid a company to put a pool safety fence around the perimeter of the pool so that my son could not fall in if he somehow managed to open the door and my sliders all have these clear plastic stoppers that fold down at the top to prevent the door from sliding open, we also have chimes on the doors so we can hear them, those came with our alarm but they sell door chimes and pool alarms to alert parents, so I think that CA must have taken some measure before and this is why she never considered that Caylee could have drowned in the early stages of her disappearance.