FULL CODE

%%[
VAR @random, @num1, @num2
SET @num1 = 1
SET @num2 = 12
SET @random = random(@num1, @num2)
]%%

%%[
%%[IF @random == "1" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/bc9aaf9b-7d0f-4ef1-a0d5-74189b5ff6ea.jpg?b=1523387048000">
%%[ELSEIF @random =="2" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/e52ececf-c3c3-4483-98d4-f92069121d20.jpg?b=1523387050000">
%%[ELSEIF @random =="3" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/c2d3d79a-dffb-4203-a41f-a02d4441a856.jpg?b=1523387050000">
%%[ELSEIF @random =="4" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/6c76fc15-1891-4d12-95c7-1dff7f7ff4db.jpg?b=1523387049000">
%%[ELSEIF @random =="5" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/21d67682-0127-4d3e-957f-aad8d9a2c382.jpg?b=1523387050000">
%%[ELSEIF @random =="6" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/f8cbacea-73e3-412e-aba9-6963633d9f69.jpg?b=1523387047000">
%%[ELSEIF @random =="7" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/f9ab44e3-a74a-4681-91fa-f81a62734234.jpg?b=1523387046000">
%%[ELSEIF @random =="8" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/1b488ad1-3cde-4bfb-a131-9658233b19ff.jpg?b=1523387048000">
%%[ELSEIF @random =="9" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/c92e8b4a-7784-4984-bd3f-0ee8d0755dcf.jpg?b=1523387049000">
%%[ELSEIF @random =="10" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/b9a31b5a-02c8-40e0-a23d-f488a8b188d3.jpg?b=1523387051000">
%%[ELSEIF @random == "11" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/530dba15-ec0c-4da7-a996-3289a883559b.jpg?b=1523387046000">
%%[ELSEIF @random == "12" THEN ]%%
 <img src="http://image.mailing.atlasprofessionals.com/lib/fe8413727c610d7f7c/m/1/89942a50-e82d-41e2-8ef0-feb49712adb2.jpg?b=1523387047000">
%%[ENDIF]%%"