Dropdown selections are used in a template grid’s searchbar for references and it seems that you want to have a template grid displaying a lsit of the image specialization records.
An option could be to associate the images to another record, display these in a template grid, but don’t use any of the associated object in the template grid itself. The the option to select the image from a dropdown would be possible.
Do keep in mind though that when large amounts of image records need to be selected by means of a dropdown will impair the performance of the page.
Not knowing the complete use case this could be a feasible option or at least provide some idea on how to move forward, I hope.