The loopj library can be used straight-forward for this purpose:
SyncHttpClient client = new SyncHttpClient();
RequestParams params = new RequestParams();
params.put("text", "some string");
params.put("image", new File(imagePath));
client.post("http://example.com", params, new TextHttpResponseHandler() {
@Override
public void onFailure(int statusCode, Header[] headers, String responseString, Throwable throwable) {
// error handling
}
@Override
public void onSuccess(int statusCode, Header[] headers, String responseString) {
// success
}
});