The film Flags of Our Fathers is a dramatic interpretation of the Battle of Iwo Jima that does contain some historical accuracies to the battle itself and war in general. Speaking of the battle, the film accurately depicts the intense fighting that occurred upon landing. American troops faced an array of fire when landing because of the loose sand on the beach causing congestion. Japanese gunfire was unleashed from the cliffs above, resulting in many casualties. The most infamous scene of the film is that of the American flag being raised on Mount Suribachi. However, it is important to note that this iconic photo was of the second flag hoisted.
As for the accuracy of the conflict in general, the film gives a true sense of the survivor's guilt and elements of PTSD that plagued the soldiers. For example, one of the main characters, Ira Hayes, is seen later in the film struggling with guilt and depression. By all accounts, Ira was never comfortable with the inevitable fame that followed the iconic photo. He eventually succumbed to alcoholism and died.
This film is considered accurate by military historians. However, I would urge you to watch the film and identify the elements of survivor's guilt and PTSD that the characters show and build your essay around that. This is the accuracy that the film succeeds with the most.