I'm glad you let us share your pain and grief, and I am so sorry for your loss of your friend. I agree with Hazel that you need a positive last image that stays with you, not the vision of your friend in the accident. It will take a while, and perhaps deliberate work on your part to bring that about.
Two things helped me, and perhaps might help you:
First, reach back into your memories for a happy time. In 2010 I held my mother in my arms as she took her last breaths, and that image stays with me. It's a sorrowful picture. But to balance that, I also have the memory of a few days before her death, when my mother gestured me to her bedside, and whispered "thank you." The first words she had spoken in many weeks, and the last she was to speak, but she managed that much for me. That picture stays with me, and is full of love. That's the sort of memory you will want to have with you as you go on from this point.
Can you picture a moment when you and your friend were laughing at something? Can you remember the sound of her laughter, the expression on her face? Try for good memories.
The memories show that your friend is with you in spirit. It's still very early days for you and it might be a while before you are able to do it, and do it without tears, but in time you might realize you are your friend's eyes and ears. Your experience of the world is your friend's.
I remember walking past a little park on my way to the grocery store, a park I would pass with my Mom so often. At first, the sight brought tears to my eyes, as I thought of my mother no longer seeing the trees, hearing the sound of children in the park, feeling the warmth of the sun on her face. Now I know she sees and hears and feels what I do. I won't say the pain is gone completely, but it is mixed with joy for having shared experiences.
You will come to that, in time. Remembering experiences shared with your friend, and remembering them with a sad / happy feeling. For now, there is pain and tears. In time, there will be smiles, too. And happier memories.
I think you have to deliberately work at it. Do you have one memory of one time you and your friend were laughing together?
The second thing that helped me was writing out my pain in a letter to my Mom after her death. I missed her terribly. Still do. There had been just the two of us for so many years, and then she was gone from sight. Somehow, though, writing to her established a new relationship, a connection that is still with me, going into four years after her passing.
For your friend, and for your eyes only, you might try a letter. It might be rambling and incoherent and tear-filled and joyous — depends on the memories it calls up. I don't use the word "closure" and I'm not sure we get to that stage after someone passes from our sight. I don't think we ever leave them behind. But I do believe we can get to a place of acceptance.
I also believe we get there each in our own way, in our own time. And it does take time. Instead of looking for pictures of your friend's last moments, can you look for pictures to hold in your mind of good times? Can you make new moments, and know you are sharing them in spirit with your friend?
I believe in something I read once: The greatest gift we can give to those who have left us is to live fully in their place. I also believe we can tell them we're doing that, and they will hear us, and know we remember them.
Let us know how it goes.