Sometimes, leaving a special video on the monitor can fix burnt-in images on an LCD monitor. Here is a YouTube video of one such video. Leave the video on for a couple hours and come back to see if the issue is resolved. Ensure the video is on full screen and that there are no black bars on the edges. Pick a different video that the beginning of the video references if you need a different resolution.
Also, ensuring that your monitor is correctly calibrated is also good! For Mac, here is a link to an Apple article that can assist you with finding out how to calibrate your monitor. Below is a quote from the Apple article:
Calibrate your display regularly to ensure accurate color.
Choose Apple menu > System Preferences, click Displays, then click Color.
Click Calibrate.
Display Calibrator Assistant walks you through calibrating your display, then creates a calibrated color profile.
For a more detailed calibration of your display, select the Expert Mode checkbox, which is at the bottom of the introductory text in the assistant.
When the display profile is ready, it’s automatically assigned as your display’s color profile.
Some displays have additional built-in color accuracy and calibration features. For more information, see the documentation that came with your display.