Text-Image.com is an online service for converting images to ASCII text art, HTML and Matrix style text. Using the service is simple, just upload the image you desired to convert it into text and select the charachters for the conversion and select other parameters like font-size, image width, color etc and then click convert to get the output.
It can convert pictures of the formats BMP, GIF, JPEG and PNG. You can save the image by taking a scrrenshot and with an image editor. If you wish to save it as a html file then you need to copy the page source. After converting the image you will get the output in text format, right click on the page and select view page source, on that source code you will see a big chunk of html code with < font > tags around, copy that and paste it wherever you wish.
If you are looking for desktop tool to convert images to ascii text checkout this lightweight image editor, it can save images in ascii text art format.