Try using
GuiShowImgCtrl instead. Not sure what you're trying to accomplish in the long run, but I'd be willing to bet that it'd be more appropriate for what you're doing.
PHP Code:
new GuiShowImgCtrl("Test_ShowImg") {
this.image = base64decode(temp.img);
}
I also know this has been pointed out to you in numerous threads, but you really oughta use variable headers all the time.