A photo (similar to the one shown) of a white lesion on the palate — what could this be?

A focal, somewhat thick white-to-red plaque localized to the palate (rather than a diffuse, bilateral, generalized pattern) is most consistent with oral candidiasis (especially in denture wearers or with other local risk factors), as opposed to white sponge nevus (which is diffuse and bilateral, usually on buccal mucosa) or leukoedema (a filmy, generalized buccal mucosa finding). SCC would typically show more induration, ulceration, or irregularity rather than this kind of plaque-like white lesion alone.