This is a great engine, I tried some test images with the mario example though and I got a black screen.
It seems on Gimp, it can palletize images with 8 colours - these are fine in Tiled - then Tilengine won't use them. So a workaround on Gimp seems to be - use a large jpeg with lots of colours, dragdrop your pixel art onto it, put it in the top left, merge down, then change the image mode, then save.
I just checked and resaving/resizing the image with Gimp afterwards works.
Amazing engine, thank you.