Two files go in this folder:

  graphics/pc/makeshift_pc.png        -- 128x128px, in-world entity sprite
                                          (2x2 tile footprint at 64px/tile hi-res)
  graphics/pc/makeshift_pc_icon.png   -- 64x64px, inventory/recipe icon

Only makeshift_pc.png is currently wired up (prototypes/data-bank.lua).
If you want the 64x64 icon used instead of the tinted vanilla combinator
icon fallback, swap the `icons` block for `makeshift-pc` in
prototypes/data-bank-items.lua to point at this file.

Different pixel size than 128x128? Change `scale` in
prototypes/data-bank.lua's `pc_picture` table to (2 * 32) / <your_width>.
