<meta http-equiv="imagetoolbar" content="no"> will stop the IE image toolbar appearing as previously said.
Just out of interest, you folks do know the easy way to hide images eh? Try this:
What you should remember is that
most folk would have no idea how to find a file in source code, if they are determined they will
eventually, but there is nothing wrong with making it harder for them.
First thing to do is get rid of any right click type interference, when I come across a site that prevents me from right clicking I go out of my way to see what they are hiding, so remove that stuff and allow them to right click all they want (Right click is a necessary tool when surfing, you should never try to disable it on someones computer anyway, it aint your computer to do so ..

)
Next make a table like so:
<table width="250" height="200" cellpadding="0">
<tr>
<td width="250" height="200" background="picture_you_want_to_hide.jpg"><img src="clear_gif_file.gif" width="250" height="200"></td>
</tr>
</table>
Anyone right clicking and trying to save the 'picture' above will only get a blank .gif, and
most people are so baffled as to why the pictures blank they give up....
Iv'e been using this method for years on certain pictures I 'treasure', and I ain't seen copies anywhere..
Give it a try, its extremely successful for such a simple fix!!