this pic is called menu2 because was taken from the startup menu logo and used for the startup screen.
To make this the startup logo:
save this picture to (open as root on the lib folder)
File system/lib/plymouth/themes/mint-logo
Than open mint-logo.script and change
logo.image = Image("menu2.png");
insead of menu2.png there will be logo.png. just change the name and save.
Next open the terminal and put: sudo update-initramfs -u

let it finish and you are good to go.
let me know if you have any questions