Changing file extensions while copying into a new sub directory C++ - c++

Question

I have a directory that contains files (mostly images) and am trying to create a new sub directory named Thumbnails that will copy all images and replace the file extension from ".jpg" || ".png" to ".thumb".
So far my code will copy all the files into the new sub directory but I can't find a way to ignore all the files that are not images (it's copying every single file in the original directory) and to change the extension of the files that where copied.
#include <iostream>
#include <filesystem>
using namespace std;
namespace fs = std::experimental::filesystem;
//Predefined Functions
void createThumbnails(string path);
int main(void)
{
string DailyFolderPath = ".../images";
createThumbnails(DailyFolderPath);
return 0;
}
void createThumbnails(string path)
{
//Create Thumbnail Sub Directory
string newThumbDir = path + "/Thumbnails";
fs::create_directories(newThumbDir);
//Copy files into Thumbnail Directory
fs::copy(path, newThumbDir);
for (const auto & p : fs::directory_iterator(newThumbDir))
cout << p.path().filename() << endl;
}

Answer 1

Your attempt proposed in comment cannot work because you are passing only filenames instead the full paths to files:
fs::copy_file(p.path().filename(), p.path().filename().replace_extension(".thumb"));
^^^^^ your app doesn't see these files
You can try something like this:
void createThumbnails(string source)
{
fs::path newThumbDir = source + "/Thumbnails";
fs::create_directories(newThumbDir);
for (const auto & p : fs::directory_iterator(source)) // iterate over all files in source dir
{
fs::path fileToCopy = p; // make copy of path to source file
if (fileToCopy.extension() == ".png" || fileToCopy.extension() == ".jpg")
{
fileToCopy.replace_extension(".thumb"); // change extension
fs::path target = newThumbDir / fileToCopy.filename(); // targetDir/name.thumb
fs::copy_file(p,target); // pass full paths
}
}
}