Under some circumstances, in my case HostMatchType = URL and non-virtual host mode, the following syntax

<img src="{$node.object.data_map.my_image.content[image_size].full_path}" ... />

does not provide a sufficient path and the image will consequently not be displayed.

In that case do the following steps:
1) check the value of the src parameter in the source code of your page
2) compare that value to the one you get by using attribute_view_gui to show my_image
3) if the difference is that the latter starts with the name of the folder eZ publish is installed in, then you should include the ezroot operator like this (note the removal of quote marks):

<img src={$node.object.data_map.my_image.content[image_size].full_path|ezroot} ... />

ps: this issue is reported in bug report no. 7917