When uploading to Imageshack, there are some option to optimize the picture by resizing them. As in a blog, it need not to be a 4096*4096 resolution. On the other hand you can use thumbnails on the blog.
If u have some image editing software like Photoshop or at least Paint.NET or IrfanView, then you can also save the file in different format like in jpg, gif and reduce the quality to reduce the file size.