I didn't actually say what i measured here, or how I computed it, did I...
I measured the screen (which is obvious as you say). Call that Y. I also measured the part you see that I measured. Call that X. then the size of the picture is X - (Y-X) = 2X-Y. Then etc. Do you see now what I did?
I guess i might as well say what I actually did.
Y is bottom of screen to top of screen. X is bottom of cable (presumed bottom of image) to top of screen.
X - (Y-X) = 2X-Y is bottom of image to top of image (assuming center placement).
image size presumably 1136. Scale that up to get the approximate vertical dimension: 1136*Y/(2X-Y).
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Does anyone know if it's possible to correct for camera lens distortion? This, followed by a linear transformation to make it appear that the photo was taken perpendicular to the screen rather than at an oblique angle, might give a more accurate resolution estimate.
I'm guessing that without knowing what camera (and in particular which lens), and without knowing exactly what the crop is, it's probably not possible to correct the distortion.