With Premium and White Label version of Easypromos it's possible to set up one period to enter the promotion by submiting pictures and another period for the voting. You can configure this option by going to Editor > General > Dates, where you'll find the different promotion dates you'll be able to set up.
In particular, to set up two different periods you should play with these two types of dates:
1. Start and end of ENTRY date: this is the date when your users will be able to enter the promotion and send their pictures.
2. Start and end of VOTING date: this is the date when users will be able to vote for the entries.
You can set up the Start of Voting date to be later than the End of Entry date, this way your users will only be able to vote once the period to submit pictures is finished.