Are you planning to do that conversion more than once?
It would be quite simple to convert that image. I don't know how many different colors are in that image, but judging by the color scheme of that image, you will only be able to use 5-7 mIRC colors. You could just copy/paste the text from that ascii image into a text editor, and then find/replace <font color="black"> with ctrl-k+01 (for example). You would do that over and over for each hex color in the string. Unfortunately, you will lose some of the color spectrum in the image due to mIRC's limited color palette.
If you are only planning to do this once, it will take a bit of time to convert, but then you are finished. Compared to the time it would take to create a script to convert it for you, you'd have the image converted manually several times over.