I tried the following
std::ifstream file("C:\\Main\\Tools\\RMXP\\RTP\\Graphics\\Tilesets\\001-Grassland01.png");
int size = FileSize("C:\\Main\\Tools\\RMXP\\RTP\\Graphics\\Tilesets\\001-Grassland01.png");
char* image = new char[size];
file.get(image, size);
sf::Image img;
img.LoadFromMemory(image, size);
But it doesn't work (Image not of any known type or corrupt), the file is okay, so what do I have to do to load an image from Memory?