Thanks for reminding me, I've been meaning to add it but kept forgetting. I now added canvas flip to 'H'. I tried to check if there were bugs left with the flipping and couldn't find any but let me know if you find any.

The prompts that are given to players are entirely controlled by the server side, so I can't affect it. The only actions that a user can do to change the prompt are are skipping the prompt and posting a doodle for the prompt, both of which give just a new prompt somewhat randomly. 

On client side it would be possible to record the skipped prompts, so you could see what prompts have you skipped but it would be impossible to try and continue those chains afterwards. Additionally dod hides the public chain id when giving the prompts, so it's not possible to directly find the url of the chain for the prompts either, if you wanted to look at the full chain you have skipped. In the experiment room the client stores the prompt data on a database so it can find the previous step, but it's limited to the experiment room and still doesn't make it possible to choose which chain to continue.

So I don't think that it would be possible to get old/skipped chains in any meaningful way. I think it would be amazing if dod would be updated with an added option for the rooms to let players select which chain they want to continue, but it's not something I can do from the client side.

Oh right, the image size the site uses is a bit weird so 100% would be 520x390px, I think the website might not save the images as png form at all. The browser renders the images based on the size of the browser window so the size varies between like 260x195(50%) and 840x630(~161.5%). 1280x960 would be ~246.2% and 1920x1440 ~369.2%. So yeah, I should probably make a proper export window that would ask for the resolution in pixels....

As for what would actually be in the final image, I think there are some very minor differences in the rendering systems of the site and on the client so the pixels near the edges of the lines might differ slightly between the two. Rendering at a higher resolution than what the site uses and scaling down with another program using e.g. bicubic scaling could give the closest result, although sometimes the renderer on the site causes moiré like patterns of its own so I don't think a perfect solution exists.

Replay preview is definitely a good idea, another window that would have a slider, play/pause and stop buttons, replay speed option and the canvas. then it would draw line segments and sleep for the rest of the frame before drawing the next batch. Should be possible. Would make animating things in dod replays easier.