This app was mentioned in 3 comments, with an average of 3.67 upvotes
There exists an app I find very useful called "eCanvas for cross-stitch", you put in any picture you like and it turns it into a pattern, and one can choose how much colors and squares it has.
It's important to experiment with both of those as they make a huge difference. (I use same cropped version image of Eleanor & Michael to illustrate, using zoomed out previews - from close up they have symbols on the pattern.)
Eg here is 27 colors vs 15 colors using the same dimensions. I know even fifteen, let alone 27 sounds overwhelming, but you won't need to really use them all in fact it shows you some only need 2 or less stitches and it's possible to press tick next to them to get rid of them. And then when you print it and look at the shades You may find say "tetra cotta" and "desert brown" are so similar shade you pick only one color (I just pencil in notes on the pattern - you can make a pdf of it to print).
As for size, this too makes a difference, here's the same image at height 50 vs height 80 , same color count. Though larger size means more stitching and each unit of ten is a square composed of 100 individual stitches.
I'd recommend no larger than 60x40 even that takes me at least two months if working at least five hours daily but I may just be excruciatingly slow :D
It can take some experimenting between a few pictures because on some no matter how high you put the count, it doesn't get the pallette quite right (I tried using the yellow dvd version of the picture and even when I kept the color number large, it focused on the clothes and made over twenty blue shades whilst making their faces one sole peach shade). It's advisable always to crop as much background as possible as that gives more squares available to focus on face details.
Best wishes :)
This looks fantastic. :) Thank you! (Play Store link for anyone who needs it.)