Generally, how deepfaking works is this:
We have 2 videos. One is the video we want to put a face in. The second video is the face we want to put into the other one. We first start by breaking each video into individual frames (or still photos, same thing). Then we detect and extract the faces from each video, and this is our "training data". After many hours (potentially 24+ hours) we use our model data to replace the face in all the frames from video 1. Finally, we convert our individual frames back to a video format.
So, yes, it is possible to use deepfaking tech to get one single picture with a swapped face. Because essentially we are swapping faces on pictures anyway, just a large amount of them at a time.
That being said, here's a few points to consider:
1. You will still need a decent amount of training data. This means you will need hundreds, if not thousands, of face pictures.
2. Deepfaking technology still has trouble with partially obscured faces (hands and hair in front of the face, eyeglasses, etc.)
3. Training for a faceswap will take hours. Sometimes over 24 hours of continuous training. If you train with CPU, it will literally take weeks.
4. Deepfaking has very specific hardware and software requirements, so not all machines will work.
5. I'm not sure if you can use just one photo in place of video 1. I've never tried it. My understanding is that you will need at least a number of photos equal to or greater than the batch size you will be using. You will still need hundreds of photos for your second dataset (video 2).
So while it is possible to get a single photo with a swapped face using deepfaking, the problem is that it's just not very efficient to do so. The extraction and conversion processes will be faster, yes, but training still takes several continuous hours. There is no way to predict how long it will take, you just have to look at the results of your training data and decide when it is ready. You still need a LOT of pictures of the faces, not just 1 or 2. You still need to meet specific hardware requirements.
The bottom line is this: due to the time involved, the amounts of data needed, and the hardware requirements, it's just going to be faster and more efficient to use Photoshop or another photo editor. If you want to spend an entire day or more to make one photo, then you certainly can do that. But in my opinion, that is a very inefficient use of time and resources. You could use Photoshop to make a convincing photo in 1/10th of the time.
And if you don't know Photoshop that well, and don't have the time to learn how to use it, well....you will discover that you will need to learn how to properly use a deepfake application too. None of this is as simple as using a mobile app. It takes time, and it takes practice. Or if you can't afford Photoshop, then you can use GIMP, which is open-source, completely free, and can do 99% of everything that Photoshop can do. There are hundreds of tutorials on Youtube and other sites for both Photoshop and GIMP.
Ultimately, how much time you want to spend to make a fake photo is your decision though.