There is no photographers stamp on the photograph
The writing on the photograph reads Start of the 1 1/8 mile now from opposite grandstand. Starting wires and boxes are removed after start. I have included this image as it shows two Julius Tote indicator boards the left one a Straight Pool Barometer Indicator and the right a Lamp Box Results and Dividends indicator. Additionally I find the wire starting system shown in the photograph rather interesting.
The barometer indicator on the left is a public display remote output device for the electromechanical mainframe of the Julius Tote. It is continually updated by the mainframe in the machine room. This display would have been driven by the Straight Pool Mainframe. The Show Pool Mainframe is shown in the first of the images in the Hialeah section of the Photo Gallery and the Straight Pool Mainframe looks the same. In the high resolution copy of this image it is possible to see the sunlight reflecting off the bulbs in the lamp panels of the right hand indicator when zoomed in on it. The information displayed on this indicator was probably manually entered via some form of control console.
The cable start system looks quite complicated with the pole on the near side of the runners with its guy wires and its suspended cables running across the runners. Judging by the horses not being lined up and there being several hoofs off the ground the photo was taken an instant after the race started. I have seen photos of this starting system before showing some horses fallen to the ground and in a tangled mess, when things have gone wrong. I have another close up photograph of the Results Board on the right. From this other photograph it is clear that this is a lamp box indicator and shows the placings 1 to 4, the Straight, Place and Show dividends and the race time in minutes, seconds and fifths of a second. The indicator accommodates a dead heat for the Straight Pool as there are two rows of lamp panels underneath the word Straight on the indicator, to display the two dividends for the runners in the dead heat. Underneath the second dividend lamp panels is the word DEAD_HEAT. This may light up when there is a dead heat.