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If you're having trouble uploading directly to the site, you can get onto a photo-hosting site. They usually give you a decent amount of free space if/when you register. (1 terabyte on Flickr, which I use, though there are other popular sites like Photobucket, Imgur and so on) Then it's a similar process: click on upload, or an upload symbol; browse through your folder of photos; and upload. Then you have to get the image link (right click and copy image address, or look about for a 'share' button. Paste the link into your post, and if the hosting site doesn't already give you the BBCode version, wrap [img] image tags around it: highlight the link text and click the 'picture in frame' button, above the line of smileys and directly below the italic
I button.
Maybe I'm a relic of dial-up and low monitor resolutions, but an image file over 1.5MB sounds fairly big! How did you resize it? Do you know what format it is? (I.e. the 'dot and three letters' at the end of the filename)