I have used the following image files with the results noted.
tif - 32bit, 300 dpi, 1811x877 pixels - will not even display, I think it is too large
tif - 24bit, 300 dpi, 359x174 pixels - best quality, but still fuzzy around curves
jpg - 24bit, 96 dpi, 359x174 pixels - worst quality of all images
png - 24bit, 359x174 pixels - fuzzy around curves
gif - 8bit, 359x174 pixels - fuzzy around curves