In your case you should use the MultipartEntity class,
MultipartEntity reqEntity = new MultipartEntity();
reqEntity.addPart("name", new StringBody(name));
reqEntity.addPart("email", new StringBody(email));
if(imagePath.trim().length() != 0) {
reqEntity.addPart("profilePic", new FileBody(new File(imagePath)));
}
HttpClient hc = new DefaultHttpClient();
HttpPost postMethod = new HttpPost(urlString);
HttpEntity resEntity;
HttpResponse response = null;
postMethod.setEntity(reqEntity);
response = hc.execute(postMethod);
resEntity = response.getEntity();
response_str = EntityUtils.toString(resEntity);