The file upload system is shit.
You can try drag-and-dropping the files directly onto the "Upload a file" area (the faint dashed rectangle below where you type your post), sometimes this works better.
If all else fails you'd need to upload your files to an image host.
Yeah I do use Flickr, it's not super convenient (well, convenient to upload photos, but takes a few clicks for each image to get to its URL) but the main reason being it's free (for 1000 pics at least), and they actually don't process / compress the files.
The file upload system is shit.
You can try drag-and-dropping the files directly onto the "Upload a file" area (the faint dashed rectangle below where you type your post), sometimes this works better.
If all else fails you'd need to upload your files to an image host.