The problem is that search engines in general are only able to read texts.
That's why even big photo sites have to make use of clear descriptions of each photo, because without the text they will not be able to index the pictures and the photos will remain unknown for the web surfer.
You need to know these limitations of search engines if you search for pictures but also when you use pictures online yourself.
The special picture search engines are developed to make the most out of the impossible conditions when searching the web for photos and other pictures.
Google and Yahoo and other big search engines (SE) have had to develop special search engines to cope with picture search.
The special search engines for pictures are making use of the file name of the pictures.
It is easy to locate picture files.
Firstly they are often located in a folder called images, because that is a widespread practice.
Secondly and more important the pictures will have one of the special extensions for pictures of which the most common are .
gif, and .
So to locate the picture files is not difficult for the SE.
The problem comes when the search engine algorithm shall estimate the content of the pictures that is what the picture is about.
If the picture has a filename like dog.
jpg it is not difficult.
But if the file name is snoopy.
jpg it is not so easy.
The SE make use of the ALT tag.
In the ALT tag an additional text is provided that is coupled to the picture when it is inserted at the webpage.
You can see the ALT text when you mouse over the picture, or if for some reason the picture is not being shown on the webpage.
The ALT text is a tool to help blind people to get information about the pictures.
As the picture search engines are picture blind as explained they will also make use of the alt text to get information about what the picture is about.
In reality only a smaller number of pictures are providing this additional information in the alt tag.
In addition to these approaches the picture search engines are using the text around the picture to estimate what the picture is about.
When a caption is obvious it should function as a source of very useful information for what the picture is showing.
In practice many captions are not so precise or useful.
You can try to take a look at a number of well visited websites and check if the pictures are easy to identify form their file name, from their alt text (if any) and from the text near to these picture.
You will probably see many examples of how these aspects on the websites could be greatly improved.
Anyway the special picture search engines are becoming better and better, and the number of indexed photos and other pictures are immense in the special search engines for images like Google Images and Yahoo Image Search.
These search engines for pictures are harvesting the pictures they find on websites and do their best to make them searchable.
You will get at mixture of thumbnail pictures of very low quality - probably the most common pictures online - and better quality photos and other pictures.
The high quality photos and pictures in general are more difficult to find or at least more difficult to sort from the mainstream use of low resolution online pictures.
High resolution pictures of professional high quality are rather difficult to locate with the picture search engines.
If you are simply interested in seeing a picture as a source of information, like you want to see a picture of an old car model, the picture SE are the first choice.
When you need to find pictures online by searching with the picture search engines you have to be aware of the limited quality of the files as most of the pictures are from amateur photographers, or even from school children.
In addition to this limitation you cannot always count on the caption to the pictures.
Maybe the car model is not the correct one stated in the caption compared to the car model shown on the picture, and so on.
Besides these considerations you have to be aware of the copyright problems you can get into.
So please use a few minutes to update your knowledge with the information below.