There are two ways to go, in a thread. (Blogs are a different story):
Plan A:
At the bottom of the area where you type your message, there is a section called "Add an Attachment" (just above the [Preview] and [Submit] buttons).
NOTE: "Attached" pictures will appear at the bottom of your message.
NOTE: Pictures smaller than 650 pixels wide will appear in your message as normal images. Pictures larger than 650 pixels wide will not appear as images, but there will be a [DOWNLOAD] button, for those who wish to see the large image, with their browser. The DOWNLOAD image size limit is 1054 pixels wide.
NOTE: You can SAVE a copy of the image to your computer and re-scale it, if it is too large, using the software linked below.
Plan B:
If the image you want is on a server now, and you can see it on your browser, it's easy.
[Img]picture's URL[/Img]
NOTE: You can have many URL images in a post, and you do not need to upload them, as in Plan A.
NOTE: The size limit on Plan B images is also 1054 pixels wide, but over 650 pixels, it starts getting obnoxious to the audience.
NOTE: You can SAVE a copy of the image to your computer and re-scale it, if it is too large, using the software linked below.
Is your picture too large (or too small) now?
http://www.softpedia.com/progDownload/GIMP-Download-5446.html
or any Gimp download site that Google finds for you. It is FREE, and very capable. The Brightness/ Contrast functions are sweet, and it has lots more functions, as well. The Gimp also comes in various flavors:
http://www.gimp.org/docs/userfaq.html#Where
For the Windows version, here is a quick-n-dirty for re-scaling an image.
[TIP: Put in a WIDTH, maybe some value less than 650 Pixels. Click in the HEIGHT box, and the correct value for that size of image will be set automagically.]
[TIP: Pictures may come out with "foggy" distortion around objects, in some sizes. Making the new image half [or twice] the original size will usually work very well.]
Avatar Creation:
Find any decent image that you like, or one that represents yourself in an interesting way.
.JPG images work well as avatars, because the file size is compressed; you can put a lot of picture into 31k as a .JPG file.
Copy and Paste your image into an empty working folder, so that the original is not going to be ruined. Do not save any changes to the original picture filename, so you can always start over again, from the first image. Changing image sizes can ruin a picture, making it grainy or weird. Starting over is a good option to have available.
You will need to shrink (Scale) the image down to a postage stamp, or really, 100 pixels (or less) in width and 150 pixels (or less) in height. The finished product must be smaller than 31k as a file size. Most graphics programs can do that job, such as Corel Photo House or Gimp. The free graphics program Gimp, referenced above, can do the Scaling job.
Then, experiment by changing the canvas size, size in pixels, pixels per inch, and file size, until you get what you want to see. Save each change with a new file name. Saving the file can cause images to lose quality, if you try to make a big file smaller during the save operation.
When you get the avatar looking the way you want it to look, save it to a handy spot such as the desktop, or a Pictures folder. The file Properties will tell you the finished size of that file.
To upload that avatar:
Click your UserName, which is in the Main Menu box, upper left corner of the Hang Gliding Org Forum Index (Recent Topics) page. That will take you to your personal Profile Settings page.
Scroll to the bottom of that page, to the Avatar Control Panel, and click the [BROWSE] button on the line "Upload Avatar from your machine." Navigate to your Avatar image, and highlight the picture that you want. Click the [OPEN] button to upload that image. The pathname to your image will be seen, next to the [BROWSE] button. Click on the [SUBMIT] button at the bottom, and it's done.
If your first try at making an Avatar is not quite right, it never costs extra to make a better one, delete the poor one, and upload the better one. This is just quick-and-dirty. Post a specific question on the HG forum, if you need more information.