Return an image from the file path with options to search multiple paths
and return a placeholder if its not found.
filepath (string) – The image filename
If a path precedes it, this will be searched as well.
dirname (string) – is the directory where the image may be located - any file at
the end will be ignored.
place_holder (bool) – if True a new place holder image will be created.
this is useful so later you can relink the image to its original data.
recursive (bool) – If True, directories will be recursively searched.
Be careful with this if you have files in your root directory because
it may take a long time.
ncase_cmp (bool) – on non windows systems, find the correct case for the file.
convert_callback (function) – a function that takes an existing path and returns
a new one. Use this when loading image formats blender may not support,
the CONVERT_CALLBACK can take the path for a GIF (for example),
convert it to a PNG and return the PNG’s path.
For formats blender can read, simply return the path that is given.