Joomla 2.5 - Adding Images to Articles from the Administrator Back-end
Login to the backend of the website by going to http://www.yourdomain.com/administrator
Enter in your username and password and hit "Submit".
From the top menu, hoover over “Content” and select “Article Manager” from the drop down menu.
Click on the title of the article you would like to add an image to or change an image on. Or you can click on the orange “New” button with a plus sign on it in the upper right corner to create a new article.
Click on the “Images and links” tab on the right side column.
The window will expand.
Click on the “Select” button to pull up your media manager.
You can upload a new image (that has been resized to 1000 pixels wide and 72 dpi/resolution) by selecting “Choose Files” at the bottom of the window.
Here is a link to an image resizing tool: http://www.picresize.com/results
Browse your computer for the resized image file and click "Open". You will see the image title in the field.
Choose the folder you want the image to go into and select “Start Upload” to add it to that folder.
Select the image. You will see the image title in the image url field.
Click on “Insert” in the upper right corner.
You will now see the title in the "Intro Image" field.
Add a keyword-rich description in the “Alt Text” field. This will not show on the site. It’s for Google’s benefit.
If you would like the image to have a caption that people can see you can add it to the “Caption” field.
Do the same thing for the “Full article image”. This image will show on the opened article. The Intro image will show in the section with a small lead-in description beneath it.
“Save” or “Save & Close” your article.