Rayman Legends

To get this achievement you'll have to break every lock that blocks the entrance (painting) to a level.
The achievement will pop when you visit the last painting that is still locked and the animation of breaking the lock is shown.

Luckily the paintings of heroes are not required for this as there is one hero that requires you to get a total amount of 1 million lums and another one that needs all 700 teensies to be unlocked.

The requirements to break these locks are twofold:

1.)
To unlock the regular levels of this game (five worlds + "Living Dead Party"), you need to collect the amount of teensies listed on the lock of its painting.
The highest amount of teensies that is necessary for a lock is 400 (to get access to the world "Living Dead Party").
You can collect teensies by rescuing them (that means to destroy their cages) in each level. Depending on the level there are either 3 or 10 teensies that you can get.
The top of the painting shows, how many teensies there are in total and how many you have collected so far.
With another playthrough you can free teensies in a level that you previously missed (teensies you already have will be golden now instead of blue, so you know which ones you don't need).
Also note that in all of the levels with 10 teensies, 2 of them are hidden in secret chambers.

2.)
The second part is to unlock all of the "Back to Origins" paintings, which are another 40 levels (5 worlds with 8 levels each).
To unlock these paintings you need lucky tickets that reward you with a "Back to Origins" paintings (there are also other rewards granted through lucky tickets: lums, creatures and teensies).

You get lucky tickets by completing single levels and worlds as a whole.
For every level where you collect 75% of the lums required for a gold score you'll receive one ticket.
The gold scores of the levels vary and are either 600, 300 or 100. So the amount of lums needed is either 450, 225 or 75 depending on the level.
To check whether you already have the lucky ticket for a certain level, just go to its painting and you'll see either a symbol of a lucky ticket next to the title of the level displayed at the bottom of the screen or only the shape of the ticket.

For every completed world you'll receive additional 5 lucky tickets (with the exception of the "Living Dead Party" world, which grants you 10 tickets).
Completing means just that you must have passed all 8 levels of the respective world (it doesn't matter if you got bronze, silver or gold on the levels).

Also note that invaded paintings are the only levels that don't reward lucky tickets.

To redeem a lucky ticket, press Y one the level select screen and go to "lucky tickets".

Unfortunately I'm not sure about the exact number of lucky tickets that are required to get the last painting unlocked, but I know that my achievement counter for collecting all lucky tickets was at 83% when I got my achievement (also I'm pretty sure that the rewards of the lucky tickets are in fixed order and should be the same for every player).

As far as I know there is a total of 157 lucky tickets.
So you should get your last painting once you have the 130th or 131st ticket.

Below you can find a list, showing how I calculated the total number of lucky tickets in the game:

10 princess levels (2 in each of the 5 worlds)
40 regular levels (8 in each of the 5 worlds)
7 "Living Dead Party" levels
40 "Back to Origins" levels (8 in each of the additional 5 worlds)
50 extra tickets for completed worlds (5 for each of the 10 worlds)
10 extra tickets for completing"Living Dead Party"

Total tickets: 157

Please leave a comment, if something is still not clear enough or if there are corrections or additions.