I don't believe you can do it with a normal showimg, but it should work with GUIs.
PHP Code:
//#CLIENTSIDE
function onCreated() {
new GuiTextCtrl("TxtObject") {
profile = GuiBlueTextProfile;
useownprofile = true;
profile.fontsize = 72;
x = y = 100;
text = "Large text";
}
}
You should explain why you need the large text to begin with because there's probably a better solution for your problem.