virtualbox.org

AFAIK the size should be 640x480 in 256 colors.

<snip>
With --bioslogoimagepath <imagepath> you can, if you are so inclined, replace the image that is shown, with your own logo.
The image must be an uncompressed 256 color BMP file without color space information (Windows 3.0 format).
The image must not be bigger than 640 x 480.
</snip>

@supercrazymark : can you confirm that you are actually reading, understanding, and trying the same information we keep posting? Because it looks to me like you don't.
And if not, I'll just have to end this topic.

@noteirak : Yes I am understanding and trying everything in this and all other topics I have created. I find this forum very useful and am not sure why you think I don't understand.... I shall be trying a 640x480 splashscreen this morning and will post back my results. Although VirtualBox is by far the best solution for having VM's on my work network I find the documentation lacking in examples and clarity, which is why I turn to the forum.

I have just tried a 640x480 .bmp file and it works perfectly, thank you to all who helped me with this

Thank you for posting the resolution, I think this thread will be more than usefull to others in the future.