terms of use
Short, because there is very little to agree about: a free page that mixes two pictures on your own machine creates few obligations in either direction.
Your pictures stay yours
Nothing you open here is licensed, claimed or acquired by this site, which would be difficult in any case since no picture is ever received. The composite you export is derived from your own files and is yours on the same terms they were. You are responsible for having the right to use both frames you put into the slots, including anyone photographed in them.
What the tool is offered as
A free page, provided as it stands, with no warranty of any kind and no undertaking that it will be available tomorrow or that it will produce a particular result. Browsers differ in how they composite pixels, which this site measures and works around rather than guarantees; a blend that matters should be checked before it is used for anything that matters. Keep your originals. Nothing here modifies a file on your disk, but a tool that has your only copy of a photograph is a bad arrangement whoever wrote it.
Reasonable use
Use it for as many pictures as you like. Do not use it to produce material that is unlawful where you are, and do not present a blended photograph as an unaltered record of an event — the whole point of this tool is that the result is not a photograph of anything.
Liability
To the extent the law where you live permits it, the operator of this site is not liable for loss arising from using it, including loss of data or of time. Where the law does not permit that limit, liability is limited to the amount you paid to use the site, which is nothing.
Which law
These terms are governed by the law of England and Wales, and nothing in them removes a statutory right you have as a consumer wherever you are reading this.