You don't need to have an imdb account, the only thing from imdb needed is the imdb url of the movie (to identify it with a number). So, let's say you want to upload pictures for Se7en (1995).
1) You go to "Add" in the upper bar
2) Inside the case "IMDb URL" you paste the URL of the movie, that would be:
3) Once the title is loaded, click "Continue"
4) Select files in your computer that you want to upload (up to 10 pictures each time). Once all are selected you clic "Upload files".
5) You fill the info:
"Category": is necessary to upload the picture, here you would have a guide about the use we have for Categories http://www.moviestillsdb.com/forum/topic/143
"People": all the actors in the picture separated by commas. If you don't recognize someone you can let it blank, the better the names are (no more, no less, no mistaken), the quickest it will be approved.
Copyright note: if you have some info about the copyright of the picture you can include it. Also some relevant comment about the picture (for example, the url of a picture you want to substitute or something). Most times people let it blank and we include a generic copyright for the entire movie based on the studio.
6) Click on "Submit images".
And that's it, you wait for moderation and see them upload and the credits added if everything is correct.
You can see I put an A), there's also a B) way to do it. If we already have some picture for that movie in our database you can skip 1) to 3). You just search the movie you like with the Search option and once in the movie profile, you clic the "Add picture" button in the upper right, so the imdb url and all that is automatically included.
Hope it helps, any doubt don't hesitate to ask 😉