[MetaCRS] plotting easting/northings

[Brian Lewis]

I have a 400x300 image taken from a map made using Lambert Conformal
Conic projection. The image is of the United States with some padding,
approximately 140W..50W, 20N..60N.

I want to plot some points of interest on the image. I convert the
latitude/longitude pairs to LCC easting/northings. But I can't figure
out how to relate the easting/northings to x/y in the image.

Any help would be greatly appreciated.