That photo isn't fake but there is very strong evidence the McCanns tampered with the metadata on the photo.
The photo wasn't released until three weeks after Madeleine's disappearance and when it was released the McCanns made a point of saying that the photo was taken the day of her disappearance (Thursday).
Someone looked at weather readings from the area during the week the McCanns were on holiday and other photos that were taken nearby that week.
The weather in the photo doesn't match up with the weather in the area on Thursday. The day was cool with moderate cloud cover. The weather does, however, match up with that recorded on the day they arrived on holiday (Sunday).
Why did they wait 3 weeks to release that photo of Madeleine? Why lie about when it was taken?