So say someone put up an illusion of a dragon. Since it's a glamer, it affects all senses. So if someone used Detect Thoughts, would the illusion fool the user into believing the illusion is a thinking creature? What kind of Intelligence score would it detect if so?
If it's a Glamer, there's something undearneath that's being "glamered". Detect Thoughts would then detect the thoughts of that creature (or corpse, or rock, or whatever).
Can you be more specific with what spell is being used? Not all illusion spells have the same effect.
If we're talking about silent image and associated spells, then detect thoughts would pick up nothing.
Silent Image is a figment though, not a glamer.