One option is to directly drag and drop your photos direcly into the post. You'll have the option of including the photo as a thumbnail or in full. I do scale/size my photos beforehand so they don't appear huge.
I just click on the "Upload a File" button. It's in the lower right corner of the posting box.
When I do that it opens a window "File Upload" and I select where my photos are located in my computer.
I do not use an online service to store my photos.
When creating a new thread/post, click the "Upload a File" button, as seen below.
In the resulting window, navigate to the files/pics that you want to upload. You can multi-select by clicking file names while holding the Ctrl key (in MS Windows. I'm not sure how to do it on a Mac but no doubt a Google search will explain it).
In the last window, select "Full Image," as below. Otherwise the pic won't display correctly.
I use imgur, too.
I think if you directly upload your photos, you can only have 10 per post. But using a third party host, I can have 35! And still I have to split my posts.