I know this has nothing to do with Ue4 but i am wondering if anybody can tell me or point me to a tutorial on how to make the background transparent for a Bmp image in Illustrator.
BMP’s do not support transparency.
You must use a format that does, such as PNG, or a format that supports and alpha channel such as TIFF or TGA.
However, if you’re just looking to mask the background in illustrator and the background is a single color, you may be able to have it live trace the image then create a clipping mask using the object corresponding to the background.