Looks like a pellicle to me. It's probably a bacterial infection, but it could also be some kind of wild yeast.
Although it's possible that you could end up with a good beer with that, the majority of accidental sours don't turn out that great. On one hand, if the recipe is one that is well-suited for a sour (for example, very low IBUs or hoppiness, relatively low alcohol/potential alcohol (if the yeast you pitched didn't ferment before the bugs took hold), little to no late hop additions, etc.), then you might end up with something pleasant-tasting. That said, since the bugs came out of the air, you don't know what's in there. It could be typical sour beer bugs (Lactobacillus, Pediococcus, Brettanomyces), but it could also have enteric bacteria and produce horrible byproducts like butyric acid (which smells like vomit). Likewise, if the environment is not suited for sours (for example: 50 IBUs, lots of flavor and aroma hop additions, and 9% ABV), then you are very unlikely to get something that will work (although it IS still possible, just... unlikely).