@Luna
the bit you wrote above, [img]i58.tinypic.com/[/img], does not appear to be a specific image link, but rather a link to the site the image was found upon. Seeing how you're based on a tablet, we can't say with 100% certainty what the means are for getting the right URL, but it could be if you hold on the image you want long enough, it'll give a pop-up box with a few options. At least that's how it is on android.
This is indeed the problem. A proper image URL ends with extensions like .png, .jpg or .gif. The
[img][/img] tags don't work if the URL you entered doesn't refer
directly to the image.
@Luna, something you could try is downloading the image you want to link to and uploading it to
imgur.com, a different website host. After uploading, you can choose from several different URLs to copy to your clipboard and one of them is the "Direct Link" URL. Put that between the
[img][/img] tags and it's guaranteed to work.