Purely as a Native English Speaker & Linguaphile I can report that - for me - the phrase "graphic image" evokes an abstract of (relatively extreme) violence or sexuality. Other uses parse as acceptable, although somewhat unusual. To wit: "graphic images of XYZ" will mean (to me) that XYZ would generally be considered disturbingly violent or sexually explicit.

Back to the OP's question: I suggest that this usage, distinct from the others also mentioned, is the result of news reports referring to such "graphic images [of violence or sexuality]" as a minor euphemism. They normally would not be willing to describe the contents in detail; rather, they fall back on the vague but still "thrilling" sounding phrase "graphic images." Over time, this became standard-ish.

Purely as a native English speaker & linguaphile I can report that - for me - the phrase "graphic image" evokes an abstract of (relatively extreme) violence or sexuality. Other uses parse as acceptable, although somewhat unusual. To wit: "graphic images of XYZ" will mean (to me) that XYZ would generally be considered disturbingly violent or sexually explicit.

Back to the OP's question: I suggest that this usage, distinct from the others also mentioned, is the result of news reports referring to such "graphic images [of violence or sexuality]" as a minor euphemism. They normally would not be willing to describe the contents in detail; rather, they fall back on the vague but still "thrilling" sounding phrase "graphic images." Over time, this became standard-ish.