Here's a way to chek your drawing's accuracy using Photoshop or PaintShopPro and layers. I hope Cindy will translate into Photoshop for me.
Take a pic of your painting in progress. Make sure you're square to the painting.
Crop a chunk to match your reference, then scale until they're the same size. This may be tricky, depending on what's already wrong. Use 2 parts that seem correct, and then just run with that. In this case, I scaled so that the top of the head and chin were at the same place, but in the past I've had to use an ear plus the chin, only to discover the whole top of the head was out of whack. Tinker with it. It'll come.
Next, let's make the photo reference a little less detailed. I used Effects> Edge Effects>Find Edges. It's just a machine - it's going to do something stupid like lose the line of the forehead where it curves back into the hair, but that is OK. That's why we're professionals.
Now I take the reference and slide it over the painting, and adjust the transparency to about 30% so that I can see the black and white ghosty, edgy photo reference superimposed over the underpainting. By turning the layer off and on repeatedly, I can go over each critical area to determine what, if anything, is wrong. Turning the layer off and on is like using tracing paper and peeking underneath repeatedly, to check if you're really seeing what you thought you were seeing.
In this case, the bottom lip and chin are in the wrong place. (I'm so glad I never finished this painting.)
Do this a couple dozen times for your drawings from photographs in early stages, and you'll find your blind spot.
Hey, is this cheating? Of course. But if I'm painting from a photo reference, the least I can do is start from an accurate drawing of the reference, and modify it from there. Luckily, the art police are just a myth used to frighten young art students.