You can find many answers to your questions in the Mapillary Help Guide. However, I am going to answer two of the questions here because answers to them may not be as apparent from the Help Guide than to the other questions.
- Can I put a watermark that says like "Visit my website → … "? Would be really cool if I can put it
No, it would not be cool. Technically, you can apply any sort of watermark because the system does not automatically filter this but legally you must not due to the Terms of Service. Attribution is already handled by CC BY-SA 4.0. Hence, there is really no need for more. However, you can add a link to your Bio in your profile (see the account dashboard). Besides, as @bob3bob3 has already mentioned, any additional synthetic image content can cause trouble in backend processing. To this end, the Terms of Service state under section 5 „Prohibited Conduct and Content”:
- Use the Mapillary Services other than for their intended purpose and in any manner that could interfere with, disrupt, negatively affect or inhibit other users from fully enjoying the Mapillary Services or that could damage, disable, overburden or impair the functioning of the Mapillary Services in any manner
- Contains any unsolicited promotions, political campaigning, advertising or solicitations
Technically, you could also use imperceptible digital watermarking (which is more difficult to do well than one may think at first glance, even with the right software) and probably no one will notice at first. However, even these imperceptible watermarks are surely going to negatively affect any AI weight data when trained on such imagery. Long story short; if you are only ready to publish your imagery with your watermark then please do not contribute to Mapillary.
- Can I upload it to another platform (g platform) and also on Mapillary?
Of course you can. You remain the author of your imagery and thus also retain all rights to it. See section 4 „User Content”, paragraph a ToS:
a. Except for the license you grant below, you retain all rights in and to your User Content, as between you and Mapillary.
However, you have to be aware that whenever you contribute to Mapillary you also always grant a license to your imagery to Mapillary by section 4 „User Content”, paragraph b ToS:
b. Without limiting your rights and our obligations under data protection law, you grant Mapillary a nonexclusive, royalty-free, irrevocable, worldwide, fully paid, transferable and sublicensable license to use, reproduce, publish, create derivative works from, distribute, publicly perform and display your User Content, for the term of its protection by intellectual property rights, and any name, username or likeness provided in connection with your User Content, for a period of ninety-nine (99) years, in each case in all media formats and channels now known or later developed without compensation to you.