Let's say you have a tiddler with an image: MyImage.jpg
Create a tiddler, say MyTemplate and tag it with $:/tags/ViewTemplate . Create it's contents like:
{{MyImage.jpg}}
Now an image will appear at the bottom of every tiddler.
Click on the tag pill "$:/tags/ViewTemplate". There will be a list of tiddlers, drag and drop MyTemplate to the top.
Now an image will appear at the top of every tiddler.
You probably don't want the image at the top of every tiddler. You need a method to flag which tiddler has the image. Let's say that only tiddlers tagged "myimage". Tag a tiddler "myimage". In "MyTemplate", edit the contents like:
<$list filter="[all[current]tag[myimage]]">
{{MyImage.jpg}}
</$list>
Now the image will appear only at the top of tiddlers tagged "myimage" .