Image of post displayed in frontpage but not in the post itself

Hello,

I have a problem working with images in my post. After lot’s of test and code manipulation this problem seems to have no issue and it makes my desperate. Help’d be very appreciate.

1./ When post content is displayed in frontpage of https://www.mysite.fr everything is ok and image is displayed correctly

2./ When I enter the post itself (www.mysite.fr/post) the image is not display anymore because WP is searching the image in https://www.mysite.fr/post/image.gif

3./ I use a function getImage($url, $filename) with a [shortcode] in the post to get the image. If the function return true then I display it with echo "<img src=\"$filename\">";

My question is quite simple, how should I define $filename for the image to be displayed in the post ? is /wp-content/images/image.gif correct ? (doesn’t work, event with directory /wp-content/images created.

If somebody can give me some help I’d appreciate a lot. Thank you