The WhatTypeImage command returns the type of an image.

If the parameter img is not of type Image, an error is raised.  The error message indicates why img is not an Image.

$\mathrm{with}\left(\mathrm{ImageTools}\right)\:$

$\mathrm{img}≔\mathrm{Create}\left(10\,10\,\left(r\,c\right)\mapsto c\cdot r\right)\:$

$\mathrm{WhatTypeImage}\left(\mathrm{img}\right)$

$\mathrm{GrayImage}$

$\mathrm{img}≔\mathrm{Create}\left(10\,10\,3\right)\:$

$\mathrm{WhatTypeImage}\left(\mathrm{img}\right)$

$\mathrm{ColorImage}$

$\mathrm{notimg}≔\mathrm{Matrix}\left(10\,10\,\left(i\,j\right)\mapsto i+j\right)\:$

$\mathrm{WhatTypeImage}\left(\mathrm{notimg}\right)$

Error, (in ImageTools:-WhatTypeImage) datatype is not float[8]