I know it's particularly difficult because of the contest format.
Normally, you would pause to catch an instant of natural life that your sharpened sensibility would capture, and from here or from the memory of this moment that reappears later, you would compose a haiku.
Generally, it happens to me as I walk, I ride a bicycle, I travel by train, rarely while driving. The compositional moment lasts a few minutes and is mental. As soon as I can, I write it in a notebook, sometimes making changes, sometimes not.
In the contest, however, the inspiring event is given by the photo, and it is not said that this photo has such an immediate and strong effect on your poetic sensibility, so you have to build on it with technique, so don't worry!