Legends of the Dead Earth was the theme of the 1996 DC Annuals. As far as I can tell, these annuals were basically a unified Elseworlds theme, but they didn't carry the Elseworlds logo (probably because DC did Elseworlds annuals in 1994, and didn't want to appear to be repeating themselves). A collection should probably have the Elseworlds logo on it though, because these stories are clearly not in DCU continuity.
For the cover, I'd go with LDK Annual #6, because the Bat-chick with the huge axe stands out every time I look at this grouping. However, I could see where DC might go with something more recognizable as Batman, so maybe Detective Annual #9, or Shadow of the Bat Annual #4.
Would you buy it? Let me know in the comments, and thanks for reading.