Yahoo messenger photo ?
If its a new photo have it ready to pick up on your desktop, unless its easy to find in your system
Open messenger window.
Left click on your avatar picture
Select "display image"
Select "share my picture"
Select "select"
Select a random picture - by clicking on it - ( to make sure it changes & your Flashplayer is ok )
Select the picture you want to display, if its not one in the gallery, click "browse" and find the photo you want - double click on it,make sure its in the display panel.
Note sometimes the image will be blacked-out. This will either be a flashplayer problem or the file you selected the photo from has numbers or / ., etc - you can try renaming the file.
Click "OK" in top photo panel
Make sure "share my picture" is still selected
Click "OK"