Compatibility with third-party sites
The images have description
The images referenced in the code of a page or TAGs include literal parameters: ALT, TITLE AND LONGDESC.
At least the ‘TAG’ ALT must be said to be indexed in search engines and aggregators as well as design guidelines of the W3C WAI standard. 
<img class = “plot” src = “/ img / diagrams / recarga_por_Paypal.png” alt = “Reload with paypal” title = “Refill with paypal” />
TITLE parameter gives the broadest compatibility (Firefox, Mozzilla) or if there is a long description:
<IMG src = “mapa_del_sitio.gif” alt = “My site Site Map” longdesc = “mapa_del_sitio.html” />
If mode is used to provide a literal object
<OBJECT Data=”lupa.gif” type=”img/gif” /> Seek </ OBJECT>
At a minimum, discuss the ‘ALT’ 20% of your images around.
For images of a typeface repeat the text: Example chart that says, “ACME SC”
<img src=”/img/logo.gif” alt=”ACME SC” />
This comment is displayed by some browsers and also helps the blind or appliances with different interfaces, to understand your site and the seers (in some browsers) to view a pop label with the text inside the ‘ALT’ (IE) or ‘ TITLE ‘(IE, Firefox ..).
Besides accessibility function, its role in marketing in spiders is relevant.
The words in the ‘ALT’ are referred to by the spiders, usually with a higher weight than other words in the body of the page. It must contain keywords.
The words in the ‘ALT’ are also used by spiders to index your images in their galleries. And if the file name matches the text of the ‘ALT’ the image is positioned above the image list when someone searches for the word or phrase on sites like yahoo or google.
<img src = “/ img / modem_cable.gif” alt = “Cable Modem: Pateco 210″
favicon.ico
Originally created by Microsoft on “Favorites icon” is used by more and more besides explorer browsers like Firefox, Mozzilla, Opera and others
The graphic file favicon.ico bitmap (16×16 pixels 16 colors) if you do not have a program to save or convert. Ips, can be created temporarily in. Gif and saved or renamed. Ico. Is invalid because the alpha channel is not appropriate but at least the server’s log is filled with errors. Replace them soon.
Must be found in the root directory or is in another included in the ‘head’ of the page:
<link rel=”shortcut icon” type=”image/x-icon” href=”/favicon.ico” />
If you are not sent in its place a file 404 (not found) and recorded in the server error log, consuming bandwidth.
For now the file is used in the URL field some browsers, others in the field favorite in the future can find many more applications.
Despite its smallness gives the URL identification and strengthening brands. Precisely because they are so small and almost unnoticed falls into that category of subliminal advertising, safe, in this case as simply associates the brand’s image.