Picture that is enthralling the old lady, first in guidebook (5)
I believe the answer is:
image
'picture' is the definition.
('image' can be a synonym of 'picture')
'that is enthralling the old lady first in guidebook' is the wordplay.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'enthralling' means one lot of letters goes inside another.
'the old lady' becomes 'ma'.
'first in' indicates taking the first letters.
The first letter of 'guidebook' is 'g'.
'ma'+'g'='mag'
'ie' enclosing 'mag' is 'IMAGE'.
(Other definitions for image that I've seen before include "Mental picture; idol" , "Iconic representation" , "Visualisation" , "Likeness or mental picture" , "Epitome" .)