for bmp:
image/x-bmp
image/x-ms-bmp

for ico:
image/icon
image/x-ico
image/ico
text/ico
application/ico
image/x-win-bitmap
image/vnd.microsoft.icon

for pcx:
image/vnd.zbrush.pcx

for ppm:
image/x‑portable‑bitmap
image/x‑portable‑graymap
image/x-portable-pixmap
image/x-portable-anymap

for tga:
image/x-targa

reference:
https://en.wikipedia.org/wiki/BMP_file_format
https://en.wikipedia.org/wiki/ICO_(file_format)
https://en.wikipedia.org/wiki/Pcx
https://en.wikipedia.org/wiki/Netpbm_format
https://en.wikipedia.org/wiki/.tga

there's also "image/x-ms-bmp"
they are results for it in search engines