I do not think it's possible to find a totally legitimate one. But it is possible to filter out those that are sure to be scam. If you have a reliable escrow, the devs you know in the community already gives you greater security. Nothing guaranteed. I recommend Google search the images they use in the ads, some use edited images of the ones that already exist on the internet 

I think if you can find out infomation of development, CEO... and the real usefull of this project. It's real.

I think ICO is regulated: meaning there is no third party protecting the funds you invest. If a company’s Initial Coin Offering (ICO) is legit can be a helpful skill to develop prior to deciding on your crypto-investment strategy. We are aiming to build Initial Coin Offerings website transparent, easy to realize and available for everyone.

I think you can find the white paper and the teammembers to see if they are reliable enough.

Do a further readings and research and also don't just rely on a single reference, much better to use a lot of references like reddit, telegram and also here in bitcointalk. And also, check the ratings of the ICO if it is going to be good or bad. Understand their whitepaper if their ideas will surely give a lot of contributions in the near future.

it may be difficult to determine the legitimate ICO and that is not because before investing in ICO we have to join the existing program of gift of ICO, and we must read white pepper to see the project, team and its development because now many ICO growing so many people say ICO it just a collect funds from investors who have joined

Well, aside those things checking whitepaper and team advisor you can see this please click tje link https://tokenmarket.net here you can see legit ICO having on going and to be launch ICO. All the details are build in to select the best ICO being develop in the blockchain.

All illegally appearing cryptographic currencies will become legal in a few months or years. will gradually be used in the shopping madness of the consumer society. 

Question, How to Find a Legit ICO?

What and Interesting Question But Its more Complicated to answer but in some Cases in other countries Like the U.S Doing and ICO or CrowdFunding is Already regulated by the Government Specifically Like S.E.C people behind those ICO's are real people and Not Hiding there Identity so in that case you can sure its legit But its different in other countries, Im just qouting U.S as and Example But not all Countries that hosting ICO's and Crowdfunding has a regulation laws or Maybe there is But They are still in Confusion of doing a regulation. BTW just be vigilant of Doing anything regarding this topic.

I think you can find the white paper, team and the roadmap.