Question about rotating image with glRotatef

i want to rotate an image around Y axis with the following code:

ofSetColor(255,255,255);
glPushMatrix();
glTranslatef(500,500,0);
glRotatef(angle,0,1,0);
im.setAnchorPercent(0.5f, 0.5f);
im.draw(0,0);
glPopMatrix();

according to my understanding, the image will become a line when angle equals to 90 degrees. however, it’s about 120 degrees when the image shrink to a line. it seems that the view piont is not perpendicular to the opengl drawing plane. is there a way to set the view point perpendicular to the opengl plane?

unless you are drawing the image right in the center of the screen it won’t look as a line, the camera is right in the center of the screen so anything that is a little to the left or the right will look as if you were looking at it from one side instead of directly straight at it.