Concat Web.config value and string in Image control SRC - asp.net

Question

I have a web.config key :
<add key="IMGSRC" value="http://localhost" />
I want to use the value of this key along with the path of the image concatenated to in an aspx page. I'm aware that I can get to root folder by simply saying "../ImagesFolder" , but my website has parent path disabled because of security concerns. So now I need to work around it.
I need something like this (Here are a few things I tried after looking up the internet and which did not work.):
1) <img id="Img19" runat="server" alt="Admin" src='<%#ConfigurationSettings.AppSettings["IMGSCR"] %>' />
2) <img id="Img19" runat="server" alt="Admin" src='<%#ConfigurationSettings.AppSettings["IMGSCR"] + "/ImagesFolder/img.jpeg" %> ' />
3)
<img id="Img19" runat="server" alt="Admin" src="<%#ConfigurationSettings.AppSettings["IMGSCR"] %> " + "/ImagesFolder/img.jpeg" />
Also I tried this:
I declared a variable Path on Page_Load
Path = System.Configuration.ConfigurationManager.AppSettings["RootforIMG"].ToString();
and then on aspx page I tried using it as
<img id="Img19" runat="server" alt="Admin" src="<%=Path %> " + "/ImagesFolder/img.jpeg" /> but this as well is no good.

Answer 1

Can you try something like below?
<img id="Img19" runat="server" alt="Admin" src='<%= GetImageSource()%>' />
In code behind
public string GetImageSource()
{
return ConfigurationManager.AppSettings["IMGSCR"] + "/ImagesFolder/img.jpeg";
}

Answer 2

The relative path of images should work:
Relative path can be as per your page location i.e: '../IMages/img.jpg' or 'images/img.jpg'
try this :
<img id="Img19" runat="server" alt="Admin" src='ImagesFolder/img.jpeg' />

Answer 3

For controls with runat="server" attribute you do not need any special code to map a path relative to web site root:
<img id="Img19" runat="server" alt="Admin" src"~/ImagesFolder/img.jpeg" />
The path ~/ImagesFolder/img.jpeg will be resolved replacing ~ with the root folder of your web-site.
If to resolve path you need some kind of logic (for example you need to call a function) then you can use this:
<img src'<%= ResolveImageName() %>' />
Do not forget that URL must be proper encoded.