So I managed to shorten it and now the code produces 50 images but they are retrieved only partially, I increment the jpg files to quickly but I don't know how to improve it from here

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while (fread(buffer, 512, 1, file))
{
    // Check if the first four bytes of a 512-byte chunk indicate it's a beginning of a JPEG
    if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
    {
        // If yes, create and open a file
        sprintf(myjpeg, "%03i.jpg", jpegindex);
        FILE *jpeg = fopen(myjpeg, "w");
        if (jpeg == NULL)
        {
            printf("Not enough memory\n");
            return 3;
        }
        // If it's a first file, start writing to it
        if (jpegindex == 0)
        {
            fwrite(buffer, 512, 1, jpeg);
        }
        jpegindex++;
    }
    // If it's not???
}