Try uploading your map(s) to
Dropbox or
Google Drive.
For Dropbox, upload it in your "Public" folder using one of the buttons (which look like this:

), then right-click the file and choose "Copy public link". Paste that here.
For Google Drive, click the little button that looks like:

Upload the file you want, and once it's done, click the little "Share" button in the upload manager box that should have popped up. Change the access level to "Anyone with the link", copy the link it gives you, and paste it here.
For images, you can try
Imgur (or alternatively also use Dropbox or Google Drive, but I haven't used those for images so I can't help there). Imgur's interface is pretty self explanatory, but if you need it, just click "upload images" at the top, then "browse your computer", find the image(s), and click "Start Upload". Once the images are uploaded, click on each of them, copy each one's URL, and paste those here in [img][ /img] tags.