Haskell Image Processing (HIP) Library provides an easy to use interface with a whole variaty of image manipulation capabilities.
Processing can be done sequentially as well as in parallel, with an inherited fusion capabily, all through <https://hackage.haskell.org/package/repa repa> and <https://hackage.haskell.org/package/vector vector> packages. It is highly extendable, with an ability to add various color spaces or provide implementations for underlying array like custom data structures.
It is capable of reading and writing a number of popular image formats by using <https://hackage.haskell.org/package/JuicyPixels JuciyPixels> and <https://hackage.haskell.org/package/netpbm netpbm> packages. Being a pure Haskell library it does not require any external programs, although it can display images using a program of your choice.