JOSM: How to annotate on top of an image?

I am currently looking into using the plugin PicLayer:

I basically want to be able to annotate on top of the image in the pixel coordinates such that (0,0) starts at the top left corner. Does this mean I need to create any .cal file to position it in a set place in the world and then scale it based on the lon, lat? Wouldn’t this cause some slight distortion error? Although I would think the distortion error is negligible as long as the image is not too large and the scaling not too extreme.

Or is there some alternative I am unaware of?

Edit: If I want to georeference the image, I think I need to create a .cal file. In such a case how do I determine the parameters of this file if I have the lon, lat information for the image?

JOSM and the PicLayer plugin are designed for mapping OSM data. They aren’t the right tool for annotating an image. Many photo editing programs have the ability to show the pixel coordinates of the mouse pointer, so you might want to try Photoshop, GIMP, or some other photo or image editing software.

So I am annotating an image that could potentially be georeferenced. I suppose in such a case I would want to create the .cal file? Since JOSM does not support geotiff or any sort of georeferenced image. But how do I define the parameters of the .cal file?