You wrote a literal string instead of concatenating the variable data onto the end of the character vector.
fullfile('C:\Users\JV\Desktop\Labeldata.imageFilename')
% ^^^^^^^^^^^^^^^^^^^^^^^^ part of literal character vector, NOT a variable!
% ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one character vector.
%^^^^^^^^ does nothing
You probably meant to do something like this:
Labeldata.imageFilename = fullfile('C:\Users\JV\Desktop',Labeldata.imageFilename);
