save image names form a loop in a new variable

Hi, i have images sets (1.png, 2.png, 3.png....) and load each image for some image detection action through a loop . If detection of img(j) is not possible then save the image name among each other in a new variable: problem_images. Look for this the else section below. The problem_images should look like this. Thank You

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clear all; close all;
    %path/directory of images
    currentpath=pwd;
    org=strcat(pwd);
    edge=strcat(pwd,'\detection');
    cd(org);
    images=dir('*.png');
    N=length(images);
    
    %doing detection stuff for all images in this folder
    for i=1:N
  
    [filepath,name,ext] = fileparts(images(i).name);
    img = imread(images(i).name);
    
        if size_lines>2
        %if image is ok, do some detection stuff...
        
        else
        %detection is not possible, save the name of the image(i) in a new variable
        problem_images(:,1)=(images(i).name);
        end
    end

Answer 1

[KALYAN ACHARJYA]

Here, I answered based on decription of the questions

j=1;
for i=1:total_images 
%Images call one by one
%Detection Part
result=....% This variable is result from detection
%Store all those image numbers (problem Images) in cell array
if isempty(result);
problem_images{j}=['Image_number',num2str(i)];
j=j+1;
end 
end

[Tommy Schumacher]

i got this error message

"Expected one output from a curly brace or dot indexing expression, but there were 0 results"