This is the 6254th most frequent Russian word.
удачное
Successful, fortunate, or favorable.
Here, 'удачное' indicates that the choice of the picnic spot was good or suitable for the activity.
Мы выбрали удачное место для пикника.
We chose a favorable spot for the picnic.
The word 'удачное' is used as an adjective meaning 'successful' or 'favorable'.
Это было удачное решение.
This was a successful decision.
The word 'удачное' describes the quality of the photo, implying it was taken well or with positive results.