solved problem this way:
sf::Http http;
http.setHost("
http://riedbook.de/");
sf::Http::Request request;
request.setMethod(sf::Http::Request::Get);
request.setUri("/images/avatar.jpg");
request.setHttpVersion(1, 1); // HTTP 1.1
sf::Http::Response response = http.sendRequest(request);
std::string body = response.getBody();
sf::Texture test;
test.loadFromMemory(body.data(),body.size());
sf::Sprite testsprite;
testsprite.setTexture(test);
Without even saving the file on my Pc temporally, i think this is a nice solution
Thinks Ixrec for idea with loadmemory D: