First, there's obviously Jaime Lannister and Bronn:
|Jaime and Bronn at Los Barruecos||Jaime and Bronn in season 6|
By closely examining the other pictures, you can make out other interesting details.
There are some pictures with two riders - one of them is definitively Randyll Tarly, riding the dapple grey horse we've seen him on before. The second, bigger one might be his son Dickon, played by actor Tom Hopper in season 7:
|Riders at Los Barruecos||James Faulkner taking riding lessons|
And finally, we can make out a new flag besides the ubiquitous Lannister banner. It's hard to make out any details, but given the fact that it is green and we have Tarlys on location, it probably is their banner:
|Green banners at Los Barruecos||Tarly soldiers and banners in season 6|
You can check out many more pictures on Twitter - again, many thanks to @RickZornow for his great photos (and his talent evading the Guardia Civil ;-) )!