Past tense of 楽しそう？

Question

In the situation where I see someone doing something and having fun I might say 楽しそう. For example, I might be standing next to a roller coaster looking at it thinking that this looks like fun. So I would say

楽しそう。乗ろう！ = This looks like fun, let's do this!

(Of course I don't know if this is a natural or correct thing to say in this case)

Now assume I am looking at someone's pictures, say, of this roller coaster. Say, they went to the fun fair today and came back and are now showing me pictures.

How can I say "It looks like you were having fun."?

Some ideas I have are

楽しそうだったね。

The problem I have is that it makes me think that the past tense verb だった refers to the 楽しそう　so that it would mean

This looked like you are having fun.

When I really want to be saying

This looks like you were having fun.

So I guess I want to put 楽しそう　into past tense but 楽しそかった sounds wrong, too.

Answer 1

To me, at least, this question is two-fold.

1. Grammatical past-tense in the purely technical sense.

2. How native speakers actually use tenses when speaking while looking at pictures.

In pure grammar:

「楽{たの}しそうだ」⇒「楽しそうだった」 and

「楽しそうです」⇒「楽しそうでした」

In reality:

The vast majority of native speakers would not use either one of the two phrases above in the past tense while looking at photos taken only earlier on the same day.

Most would say:

「楽しそう（ね/だね/ですね）」 as if it were happening right this minute.

Furthermore, we would actually say the same even if the pictures were from a few years ago or even 50 years ago. Photos stop time in us at least temporarily and if time stops, tenses will go as well.

If you absolutely must use a past tense of some sort in saying this, one option would be to say:

「楽しかったみたいね。」 without using 「そう」.

The form you used at the end 「楽しそかった」 does not exist.