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ImageQ

ImageQ[image]
yields True if image has the form of a valid Image object, and False otherwise.
A valid image object:
An expression with head Image that is not a valid image object:
A valid image object:
In[1]:=
Click for copyable input
Out[1]=
 
An expression with head Image that is not a valid image object:
In[1]:=
Click for copyable input
Out[1]=
An expression of the form Graphics[Raster[...}] is not a valid image object:
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