Convert pnm to ithmb Online: pnm2ithmb
You can use Tom's Editor to easily convert images from
Portable aNy Map .PNM to iPod Thumbnail
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
PNM images are uncompressed 24 bit RGB images. Can cannot store Alpha channel. PNM images come in 2 types: binary and text. Especially popular on Linux.
ITHMB are thumbnails used by various Apple devices. At first these images were used by iPhods but now can be found on iPhones and iPads.