Moved this post and your other one to the regular IGM forum because these aren't tutorials.
Check the dimensions of the image you are trying to import. Both length and width should be a multiple of 8 for the best results (this can be any combination like 8x16, or 64x32, etc.). After that, it's just a matter of making sure that the tiles on your image fall properly between the lines when split up in IGM.
Hope that helps!