I was about to suggest XPaint as being equally simple, but it might be more complex than I thought:
> Recent versions have support for advanced image manipulations (image zooming and resizing, filters, color modifications, separation of RGB channels), scripting, layers, edition of alpha channel and of transparent images, vector formats import, truetype fonts and anti-aliasing, geometric transformations of such fonts, etc. …
> The scripting capabilities include programmable filters, batch processing, creation of 2D and 3D images, etc. XPaint also recently acquired a built-in editor which can be used to produce posters containing text and images.
https://en.wikipedia.org/wiki/XPaint